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Read the following passage and mark the letter A, B, C, or D on your answer answer to each of the questionsAn air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely . Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to...
Đọc tiếp

Read the following passage and mark the letter A, B, C, or D on your answer answer to each of the questions

An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely . Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled – a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions. Many of more important air pollutants such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentrations of these pollutants were altered by various chemical reactions; they became components in biogeochemical cycle. Theseserve as an air purification scheme by allowing the compounds to move from the air to the water or soil on a global basis, nature's output of these compounds dwarfs that resulting from human activities.

However, human production usually occurs in a localized area, such as a city. In this localized regions, human output may be dominant and may temporarily overload the natural purification scheme of the cycle. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, as a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

What does the passage mainly discuss?

A. The economic impact of air pollution

B. What constitutes an air pollutant

C. How much harm air pollutants can cause

D. The effects of compounds added to the atmosphere

1
22 tháng 8 2019

Đáp án: C

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 30 to 34. An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth...
Đọc tiếp

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 30 to 34.

An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled - a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities.

However, human production usually occurs in a localized area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area.

What does the passage mainly discuss?

A. The economic impact of air pollution.

B. What constitutes an air pollutant. 

C. How much harm air pollutants can cause. 

D. The effects of compounds added to the atmosphere.

1
21 tháng 5 2019

Chọn B.

Đáp án là B.

Giải thích: Bài văn chủ yếu bàn về :

A. Tác động về mặt kinh tế của ô nhiễm không khí

B. Những gì hợp thành 1 tác nhân ô nhiễm không khí

C. Mức độ nguy hại mà chất ô nhiễm gây ra

D. Ảnh hưởng của các hợp chất bị thêm vào không khí

17 tháng 6 2019

Đáp án: D

Giải thích: Ở câu "Slang, however, refers to words and expressions understood by a large number of speakers but not accepted as appropriate formal usage by the majority.", tác giả có nhắc đến “Tiếng lóng chỉ từ ngữ và cách diễn đạt nhiều người hiểu nhưng không được phần đông chấp nhận là ngôn ngữ trang trọng.”

Read the following passage and mark the letter A, B, C, or D on your answer answer to each of the questionsAn air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to...
Đọc tiếp

Read the following passage and mark the letter A, B, C, or D on your answer answer to each of the questions

An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled – a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions. Many of more important air pollutants such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentrations of these pollutants were altered by various chemical reactions; they became components in biogeochemical cycle. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil on a global basis, nature's output of these compounds dwarfs that resulting from human activities.

However, human production usually occurs in a localized area, such as a city. In this localized regions, human output may be dominant and may temporarily overload the natural purification scheme of the cycle. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, as a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

What does the passage mainly discuss?

A. The economic impact of air pollution

B. What constitutes an air pollutant

C. How much harm air pollutants can cause

D. The effects of compounds added to the atmosphere

1
13 tháng 10 2018

Đáp án C

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions from 55 to 64.      An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established inEngland in...
Đọc tiếp

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions from 55 to 64.

      An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established inEngland in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled - a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

      Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities.

      However, human production usually occurs in a localized area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, has a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

Which of the following is best supported by the passage?

A. To effectively control pollution, local government should regularly review their air pollution laws 

B. One of the most important steps in preserving natural lands is to better enforce air pollution laws 

C. Scientists should be consulted in order to establish uniform limits for all air pollutants. 

D. Human activities have been effective in reducing air pollution.

1
22 tháng 7 2018

 Đáp án : D

Ở đoạn cuối, người viết có nói khá nhiều về việc các hành động của con người ảnh hưởng tới vấn đề ô nhiễm không khí “human production”, “human output’,… =>D

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions from 22 to 28.An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the...
Đọc tiếp

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions from 22 to 28.

An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled - a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities.

However, human production usually occurs in a localized area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, has a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm

Which of the following is best supported by the passage?

A. To effectively control pollution, local government should regularly review their air pollution laws.

B. One of the most important steps in preserving natural lands is to better enforce air pollution laws

C. Scientists should be consulted in order to establish uniform limits for all air pollutants

D. Human activities have been effective in reducing air pollution

1
12 tháng 12 2017

Đáp án D

Đề: Ý nào sau đây được bổ trợ tốt nhất bởi bài luận?

A. Để kiểm soát ô nhiễm một cách hiệu quả, chính phủ địa phương cần thường xuyên xem xét lại các luật về ô nhiễm môi trường của họ.

B. Một trong các bước quan trọng nhất trong việc bảo tồn đất đai tự nhiên là thi hành tốt hơn các luật về ô nhiễm môi trường.

C. Các nhà khoa học nên được hỏi ý kiến để thiết lập những giới hạn đồng bộ cho mọi chất gây ô nhiễm không khí.

D. Các hoạt động của con người đã và đang có hiệu quả trong việc giảm thiểu ô nhiễm không khí.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 30 to 34. An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth...
Đọc tiếp

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 30 to 34.

An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled - a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities.

However, human production usually occurs in a localized area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area.

According to the passage, human-generated air pollution in localized regions ___.

A. can be dwarfed by nature’s output of pollutants

B. can overwhelm the natural system that removes pollutants 

C. will damage areas outside of the localized regions 

D. will react harmfully with natural pollutants

1
1 tháng 8 2017

Chọn B.

Đáp án là B.

Giải thích: 

Đoạn 3: However, human production usually occurs in a LOCALIZED area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles.

Read the following passage and mark the letter A,B,C or D on your answer sheet to indicate the correct answer to each of the questions from 55 to 64An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth...
Đọc tiếp

Read the following passage and mark the letter A,B,C or D on your answer sheet to indicate the correct answer to each of the questions from 55 to 64

An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled - a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities.

However, human production usually occurs in a localized area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, has a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm

Which of the following is best supported by the passage?

A. Scientists should be consulted in order to establish uniform limits for all air pollutants.

B. One of the most important steps in preserving natural lands is to better enforce air pollution laws.

C. Human activities have been effective in reducing air pollution.

D. To effectively control pollution, local government should regularly review their air pollution laws.

1
23 tháng 5 2018

Đáp án là C

Câu 1 đoạn 1 “compound added directly or indirectly by humans to the atmosphere” phức hợp của việc tác động trực tiếp hay gián tiếp đến không khí. -> hành động của con người ảnh hưởng đến việc giảm ô nhiễm không khí.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 34 to 40. An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth...
Đọc tiếp

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 34 to 40.

An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adverselyAir pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled - a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities. However, human production usually occurs in a localized area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, has a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

Which of the following is best supported by the passage?

A. To effectively control pollution, local government should regularly review their air pollution laws

B. One of the most important steps in preserving natural lands is to better enforce air pollution laws

C. Scientists should be consulted in order to establish uniform limits for all air pollutants

D. Human activities have been effective in reducing air pollution

1
10 tháng 1 2018

D

 Dòng nào dưới đây ủng hộ nhiều nhất cho bài văn ?

A.   Để kiểm soát ô nhiễm tốt hơn, chính phủ khu vực cần thường xuyên xem lại các luật lệ ô nhiễm không khí

B.   Một trong những bước quan trọng trong bảo tồn nguồn đất tự nhiên là áp dụng tốt hơn luật về ô nhiễm không khí

C.   Các nhà khoa học cần được tham khảo ý kiến để thiết lập 1 giới hạn chung cho mọi nhân tố ô nhiễm không khí

D.   Hoạt động của con người đã có hiệu quả trong việc giảm thiểu ô nhiễm không khí

=> Đáp án D

Dịch bài

          Một tác nhân gây ô nhiễm không khí được định nghĩa là 1 hợp chất bị thải vào không khí trực tiếp hoặc gián tiếp bởi con người với số lượng đủ để ảnh hưởng đến con người, động vật, thực vật, hay những nguyên liệu khác một cách đáng kể. Ô nhiễm không khí cần có 1 định nghĩa linh hoạt cho phép những thay đổi liên tục. Khi luật về ô nhiễm không khí được thiết lập ở Anh vào thế kỉ 14, các tác nhân gây ô nhiễm không khí bị giới hạn là những hợp chất có thể nhìn thấy hay ngửi thấy – khác xa với danh sách kéo dài những hợp chất được biết đến ngày nay. Khi công nghệ càng phát triển và kiến thức về nhiều hoá chất trên lĩnh vực sức khoẻ ngày càng gia tăng, danh sách các tác nhân ô nhiễm không khí đã dài hơn rất nhiều. Trong tương lai, thậm chí sự bốc hơi nước cũng bị coi là 1 tác nhân gây ô nhiễm không khí dưới những điều kiện nhất định.

          Nhiều tác nhân ô nhiễm, như SO2, CO2, NO được tìm thấy trong tự nhiên. Khi Trái đất phát triển, sự tập trung vào các nhân tố gây ô nhiễm này bị thay đổi bởi các phản ứng hoá học, chúng trở thành những phần tử nằm trong chy kỳ hoá sinh. Những phần tử này hoạt động như 1 chu trình làm sạch không khí bằng cách cho phép các hợp chất này di chuyển từ không khí sang nước hay đất. Trên nền tảng toàn cầu, sản lượng tự nhiên của những hợp chất này là kết quả từ quá trình sinh hoạt của con người.

          Tuy nhiên, sản phẩm của con người thường xuất hiện trong một khu tách biệt, như trong 1 thành phố. Trong 1 vùng như thế, sản lượng chất thải sinh hoạt thường chiếm ưu thế và tạm thời có thể vượt quá chu trình làm sạch tự nhiên . Kết quả là 1 lượng gia tăng các hoá chất độc hại trong không khí. Sự tập trung gây xuất hiện những tác động sẽ lớn hơn sự tập trung mà những nhân tố gây ô nhiễm có thể có nếu không có hoạt động sinh hoạt của con người. Sự tập trung thực tế không nhất thiết phải lớn đủ để 1 hợp chất trở thành 1 nhân tố gây ô nhiễm; thực tế, giá trị về mặt số liệu cho chúng ta biết rất ít cho đến khi chúng ta biết những con số này biểu thị cho mức độ gia tăng lớn như thế nào dựa vào sự tập trung xảy ra tự nhiên trong khu vực. Ví dụ, SO2 và những ảnh hưởng sức khoẻ có thể tìm thấy ở mức độ 0.08 ppm, gấp 400 lần mức độ bình thường. Tuy vậy, CO có mức độ là 0.1 ppm và nó không thường trở thành 1 tác nhân cho đến khi mức độ của nó đạt đến khoảng 15 ppm.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 34 to 40.An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth...
Đọc tiếp

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 34 to 40.

An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled - a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities.

However, human production usually occurs in a localized area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, has a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

Which of the following is best supported by the passage?

A. To effectively control pollution, local government should regularly review their air pollution laws

B. One of the most important steps in preserving natural lands is to better enforce air pollution laws

C. Scientists should be consulted in order to establish uniform limits for all air pollutants

D. Human activities have been effective in reducing air pollution

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5 tháng 4 2017

Chọn D

Những ý kiến nào có trong bài viết:

A. Để kiểm soát ô nhiễm hiệu quả, chính quyền địa phương nên thường xuyên xem xét lại luật về ô nhiễm không khí của họ.

B. Một trong những bước quan trọng nhất trong việc bảo tồn đất tự nhiên là thực thi tốt hơn luật về ô nhiễm không khí.

C. Các nhà khoa học nên được tư vấn để thiết lập các giới hạn thống nhất cho tất cả các chất gây ô nhiễm không khí.

D. Các hành động của con người đã có hiệu quả trong việc giảm ô nhiễm không khí