K
Khách

Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.

II/ Read the text and choose the best answers A, B, C or D. to the questions. (1m) Most of the countries in the world have searched for alternative sources of energy in various directions. Many communities are burning garbage and other biological waste products to produce electricity. Converting waste products to gases or oil is also an efficient way to dispose of waste. Experimental work is being done to derive synthetic fuels from coal, oil, shale and coal tars. But today that...
Đọc tiếp

II/ Read the text and choose the best answers A, B, C or D. to the questions. (1m)

Most of the countries in the world have searched for alternative sources of energy in various directions. Many communities are burning garbage and other biological waste products to produce electricity. Converting waste products to gases or oil is also an efficient way to dispose of waste.

Experimental work is being done to derive synthetic fuels from coal, oil, shale and coal tars. But today that process has proven expensive. Other experiments are underway to harness power with giant windmills. Geothermal power heat from the earth is also being tested.

Some experts expect utility companies to revive hydroelectric power derived from streams and rivers. Fifty years ago hydroelectric power provided one third of the electricity used in the United States, but today it supplies only five percent. The oceans are another potential source of energy. Scientists are studying ways to convert the energy of ocean currents, tides, and waves to electricity. Experiments are also underway to make use of the temperature differences in ocean water to produce energy.

1. Which is the best title of the passage?

A. The use of water productions for energy

B. Efficient ways of disposing of waste

C. The search for Alternative Sources of Energy

D. New Discoveries in Geothermal Power

2. Fifty years ago one third of the electricity in the United States was provided by_________.

A. wind B. waste products C. oil D. water

3. In the second paragraph, the phrase “synthetic fuels” could be best replaced by which of the following _________.

A. biological fuels B. artificial made fuels

C. low burning fuels D. fast burning fuels

4. Which of the following is NOT mentioned in the passage as an alternative source of energy?

A. electricity B. burning of garbage

C. geothermal power D. synthetics fuels

5. According to the author, the impracticability of using coal, oil shale and coal tars as sources of energy is due to _________.

A. their being money consuming B. their being time consuming

C. the scarcity of sources D. the lack of technology

2
4 tháng 1 2020

1. C

2.

3. B

4. A

5. A

4 tháng 1 2020

cau 2 la dap an nao

3 tháng 9 2017

choose the word or phrase which best completes each sentence

1.the weather has turned ___

a. coldly and windly

b. coldly and windy

c. cold and windy

d. cold and windy

2. Nobody is ready____?

A. is he

B. isn't he

C. are they

D. aren't they

3. he was pleeased to have the_______ to hear such a fine musician play his favorite piece of music

a. occasion

b. possiblity

c. opportunity

d. fate

4. ____ I had met him twice before, I didn't recognise him

A. Although

B. however

c. If

d. But

5. I wish you'd stop chatting àn___ with some work

A. get down

b. get on

c. come onn

d./ come back

3 tháng 9 2017

choose the word or phrase which best completes each sentence

1.the weather has turned ___

a. coldly and windly

b. coldly and windy

c. cold and windyly

d. cold and windy

2. Nobody is ready____?

A. is he

B. isn't he

C. are they

D. aren't they

3. he was pleeased to have the_______ to hear such a fine musician play his favorite piece of music

a. occasion

b. possiblity

c. opportunity

d. fate

4. ____ I had met him twice before I didn't recognise him

A. Although

B. however

c. If

d. But

5. I wish you'd stop chatting àn___ with some work

A. get down

b. get on

c. come onn

d./ come back

Air (1)...is caused of ill health in human being.....(2) a lot of countries, there (3) .....laws limiting the amount of smoke Wich a factories can (4).... although there is not enough information on the effects of smome on the atmosphere....(5) have proved that air pollution causes lung disease s. The gases from exhausts of cars have also ....( 6) air Pollution in most cities . The lead in petrol produces a poisonous gas , Wich is often ....(7) in busy streets circled by high buildings ....
Đọc tiếp

Air (1)...is caused of ill health in human being.....(2) a lot of countries, there (3) .....laws limiting the amount of smoke Wich a factories can (4).... although there is not enough information on the effects of smome on the atmosphere....(5) have proved that air pollution causes lung disease s. The gases from exhausts of cars have also ....( 6) air

Pollution in most cities . The lead in petrol produces a poisonous gas , Wich is often ....(7) in busy streets circled by high buildings . Children ....(8) live in areas where there is ....(9) lead in the atmosphere can not think as ...(10) as other children , and are clumsy when they use their hands

1 a,pollute

b.pollution

C. Polluted

D. Polluting

2 a, on

B,at

C, for

D,in

3 a,is

B, are

C, was

D, were

4 a, to produced

B, produced

C, producing

D,produce

5 a, singers

B, teachers

C, doctors

D, engineers

6 increase

B increasing

C, to crease

D, increase

7 a collected

B, collect

C, collecting

D, collects

8 who

B, which

C, what

D,why

9 a, lot of

B,a lot of

C,a lots

D, a lots of

10 a, more quickly

B, quick

C, quickly

D, quicker

2
14 tháng 6 2019

Air (1)...is caused of ill health in human being.....(2) a lot of countries, there (3) .....laws limiting the amount of smoke Wich a factories can (4).... although there is not enough information on the effects of smome on the atmosphere....(5) have proved that air pollution causes lung disease s. The gases from exhausts of cars have also ....( 6) air

Pollution in most cities . The lead in petrol produces a poisonous gas , Wich is often ....(7) in busy streets circled by high buildings . Children ....(8) live in areas where there is ....(9) lead in the atmosphere can not think as ...(10) as other children , and are clumsy when they use their hands

1 a,pollute

b.pollution

C. Polluted

D. Polluting

2 a, on

B,at

C, for

D,in

3 a,is

B, are

C, was

D, were

4 a, to produced

B, produced

C, producing

D,produce

5 a, singers

B, teachers

C, doctors

D, engineers

6 increase

B increasing

C, to crease

D, increased

7 a collected

B, collect

C, collecting

D, collects

8 who

B, which

C, what

D,why

9 a, lot of

B,a lot of

C,a lots

D, a lots of

10 a, more quickly

B, quick

C, quickly

D, quicker

14 tháng 6 2019

Air (1)...is caused of ill health in human being.....(2) a lot of countries, there (3) .....laws limiting the amount of smoke Wich a factories can (4).... although there is not enough information on the effects of smome on the atmosphere....(5) have proved that air pollution causes lung disease s. The gases from exhausts of cars have also ....( 6) air

Pollution in most cities . The lead in petrol produces a poisonous gas , Wich is often ....(7) in busy streets circled by high buildings . Children ....(8) live in areas where there is ....(9) lead in the atmosphere can not think as ...(10) as other children , and are clumsy when they use their hands

1 a,pollute

b.pollution

C. Polluted

D. Polluting

2 a, on

B,at

C, for

D,in

3 a,is

B, are

C, was

D, were

4 a, to produced

B, produced

C, producing

D,produce

5 a, singers

B, teachers

C, doctors

D, engineers

6 increased

B increasing

C, to crease

D, increase

7 a collected

B, collect

C, collecting

D, collects

8 who

B, which

C, what

D,why

9 a, lot of

B,a lot of

C,a lots

D, a lots of

10 a, more quickly

B, quick

C, quickly

D, quicker

24 tháng 6 2018

1. We should participate in the movements ___ the natural environment.

A. organizingto conserve B. organized conserving

C. organized to conserve D. which organize to conserve

2. Certifications provide proofs of your ___.

A. qualifications B. diplomas C. ambitions D. qualities

3. Prices continued to rise while wages remained low ___ the Government became increasing unpopular.

A. on condition that B. with the result that C. provided that D. in order that

4. There is ___ to be a serious energy crisis in the next century.

A. reputed B. known C. foreseen D. bound

5. ___ in that subject, I would learn more about it.

A. Were I B. If I am C. Should I D. I was

24 tháng 6 2018

1. We should participate in the movements ___ the natural environment.

A. organizingto conserve B. organized conserving

C. organized to conserve D. which organize to conserve

2. Certifications provide proofs of your ___.

A. qualifications B. diplomas C. ambitions D. qualities

3. Prices continued to rise while wages remained low ___ the Government became increasing unpopular.

A. on condition that B. with the result that C. provided that D. in order that

4. There is ___ to be a serious energy crisis in the next century.

A. reputed B. known C. foreseen D. bound

5. ___ in that subject, I would learn more about it.

A. Were I B. If I am C. Should I D. I was

4 tháng 4 2017

The wind is blowing and the sky ....................gray

a. looks b . look c . is looking d. is looks

we may know the land very well , but we know very .......about the oceans

a. few b . little c. much d. a little

cheese , butter and cream are ...

a. fruits b / vegetables c. dairy products d.milk products

1. ------ the 7-day trial period has ended, customers are welcome to return all equipment for a full refund. A. Beyond B. During C. Between D. After 2. Over the past three years, Milton Cosmetics has increased its annual revenue to its ------ level in two decades. A. highest B. widest C. most expensive D. most gradual 3. Employees are not eligible to apply for insurance...
Đọc tiếp

1. ------ the 7-day trial period has ended, customers are welcome to return all
equipment for a full refund.

A. Beyond B. During C. Between D. After

2. Over the past three years, Milton Cosmetics has increased its annual revenue to its
------ level in two decades.

A. highest B. widest C. most expensive D. most gradual

3. Employees are not eligible to apply for insurance benefits until they have been
employed ------ a period of 30 days.

A. since B. about C. for D. while

4. Product samples and giveaways are valuable ------ for companies advertising a
new product line.

A. compensation B. productivity C. growths D. tools

5. The agency is having difficulty attracting overseas customers ------ their products
are equal in quality to many of their international competitors.

A. such that B. in addition to C. by means of D. even though

6. Please return signed forms along with copies of two forms of identification to the
head office using the mailing label ------

A. provides B. provided C. is provided D. providing

7. There is a meeting for all committee members in the board room at ------ 10 a.m.
tomorrow.

A. generously B. generally C. approximately D. slightly

8. Over the weekend, a new cooling system will be installed throughout the building
which is designed to ------ energy.

A. compare B. accomplish C. avoid D. conserve

9. Recommendations for promotions will be discussed and reviewed in ------ with our
policy.

A. accordance B. accord C. according D. accorded

10. All of the new make-up products should ------ at the front of the health and beauty
department so they are easily spotted by shoppers.

A. have displayed B. displays C. displaying D. be displayed
1
27 tháng 11 2017

1. ------ the 7-day trial period has ended, customers are welcome to return all
equipment for a full refund.

A. Beyond B. During C. Between D. After

2. Over the past three years, Milton Cosmetics has increased its annual revenue to its
------ level in two decades.

A. highest B. widest C. most expensive D. most gradual

3. Employees are not eligible to apply for insurance benefits until they have been
employed ------ a period of 30 days.

A. since B. about C. for D. while

4. Product samples and giveaways are valuable ------ for companies advertising a
new product line.

A. compensation B. productivity C. growths D. tools

5. The agency is having difficulty attracting overseas customers ------ their products
are equal in quality to many of their international competitors.

A. such that B. in addition to C. by means of D. even though

6. Please return signed forms along with copies of two forms of identification to the
head office using the mailing label ------

A. provides B. provided C. is provided D. providing

7. There is a meeting for all committee members in the board room at ------ 10 a.m.
tomorrow.

A. generously B. generally C. approximately D. slightly

8. Over the weekend, a new cooling system will be installed throughout the building
which is designed to ------ energy.

A. compare B. accomplish C. avoid D. conserve

9. Recommendations for promotions will be discussed and reviewed in ------ with our
policy.

A. accordance B. accord C. according D. accorded

10. All of the new make-up products should ------ at the front of the health and beauty
department so they are easily spotted by shoppers.

A. have displayed B. displays C. displaying D. be displayed
Mark the letter A, B, C or D on your answer sheet to indicate the word whose underlined part differs from the other three in pronunciation in each of the following questions. 1. A. doubt B. suburb C. plumber D. climb 2. A. monthly B. sunbathing C. southern D. weather Mark the letter A, B, C or D on your answer sheet to indicate the word that differs from the other three in the position of primary stress in...
Đọc tiếp

Mark the letter A, B, C or D on your answer sheet to indicate the word whose underlined part differs from the other three in pronunciation in each of the following questions.

1. A. doubt B. suburb C. plumber D. climb

2. A. monthly B. sunbathing C. southern D. weather

Mark the letter A, B, C or D on your answer sheet to indicate the word that differs from the other three in the position of primary stress in each of the following questions.

3. A. efficiency B. profitable C. considerate D. mysterious

4. A. occur B. pollute C. typhoon D. access

Mark the letter A, B, C or D on your answer sheet to indicate the underlined part that needs correcting in each of the following questions.

5. Youngster nowadays (A) often (B) pay much attention (C) to physical attractive (D).

6. Although (A) her severe (B) pain, she tried to walk to (C) the auditorium to attend (D) the lecture.

7. Those students are trying their (A) best (B) in order that (C) get (D) the scholarship.

Mark the letter A,B, C or D on your answer sheet to indicate the correct answer to each of the following questions.

8.His doctor _____ him to eat less and do more exercise.

A. said B. suggested C. advised D. insisted

9. The curriculum at the public school is as good ____ of any private school.

A. or better than B. as or better that

C. as for better than that D. as or better than those

10. It’s ____ a box for me to lift by myself so I think I need some help with this.

A. big B. too big C. very big D. such big

11. He is _____ from a cut in his finger.

A. blooding B. bleeding C. blood D. bloody

12. The boss doensn't criticize other people like that. Why does he have to run her _____ all the time?

A. down B. over C. up D. in

13. Have you been to the new shopping centre on the ____ of town?

A. centre B. middle C. outskirts D. suburbs

14. We'll let you buy a motorbike _____ you ride it carefully.

A. as if B. whenever C. although D. as long as

15. There are some parts of the word _______ even now people cannot live.

A. to whom B. which C. that D. where

16. He enjoys _______ tennis and keeps on ______ sensibly; that's why he is fit.

A. playing - eating B. playing - to eat

C. to play - to eat D. to play - eating

Mark the letter A, B, C or D on your answer sheet to indicate the most suitable response to complete each of the following exchanges.

17. "What an attractive hair style you have got, Mary!" -"______"

A. Thank you very much. I am afraid. B. You are telling a lie.

C. Thank you for your compliment. D. I don't like your sayings.

18. "______"- "Oh, it's great!"

A. How is the journey like? B. Would you like the journey?

C. What do you like about the journey? D. What do you think of the journey?

Mark the letter A, B, C or D on your answer sheet to indicate the word(s) CLOSEST in meaning to the underlined word(s) in each of the following questions.

19. In 1989, a ban was given on all international trade in ivory.

A. a destruction B. an allowance C. an exploitation D. a prohibition

20. The factory is fined for discharging dangerous chemicals into the river.

A. releasing B. decreasing C. increasing D. keeping

Mark the letter A, B, C or D on your answer sheet to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following question.

21. Punctuality is imperative in your new job.

A. Being efficient B. Being courteous C. Being late D. Being cheerful

22. Pure water is often a fairly rare commodity that requires significiant energy to produce.

A. clean B. contaminated C. fresh D. flawless

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks.

Most birds build nests in which thay lay their eggs, but the emperor penguin has no need of them. This bird lives in Antarctica and must endure (23) ______ weather than anywhere else in the world. In order to (24) ______ that its eggs are not harmed and that its chicks may hatch from them, the emperor penguin take care of its eggs on a unique manner. An emperor penguin female lays a single egg. Once she lays the egg, the male penguin takes it and puts it (25) ______. There, the egg (26) _____ by a layer of stomach fat that the penguin rests above the egg. Since emperor penguins lay their eggs right as winter begins in Antarctica, it is vital that the eggs remain protected from the elements. Therefore, for the next two months, the males incubate the eggs until the chicks finally hatch. During this entire (27) ______, the maes look after the eggs while hardly even moving.

23. A. harsher B. the harshest C. as hard as D. much of the hardest

24. A. ensure B. promise C. recall D. trust

25.A. on top of its feet B. with its feet at the top

C. by the top foot D. at the foot of the top

26. A. protects B. is protecting C. is protected D. will protect

27. A. period B. periods C. periodical D. periodically

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.

I'm 18 years old and have never played on a sports team before, so I never received lessons or training of any kind. I wish my parents has signed me up for soccer when I was younger because I discovered that I wanted to play sports. I just have no skills. There is a soccer team at my high school, but I difinitely won't make it. Most people on the team have probably been playing for years. I feel like I missed my chance and that I'll never be as good as them. Is it too late for me to learn to play from scratch? I just figure that by the time I become "good", I'll be too old anyway. I tried teaching myself in the past, but it seemed too unorganized and I didn't know what I was doing. Is there some place tha teaches people of any age how to play soccer?

28. Why does the writer write this passage?

A. He wants to study how people play soccer.

B. He is trying to apply for a soccer team.

C. He needs advice on whether he should start learning soccer.

D. He has received a sport award for playing in a soccer game.

29. What can be inferred from the passage about the writer ?

A. His parent forgot to sign up the writer for a soccer team.

B. He has never played on a soccer team before.

C. His friends have all participated in some sports teams.

D. He envies those who can play soccer well.

30. In line 7 , the word 'figure' is closet in meaning to _______.

A. think B. want C. trust. D. choose

31. In line 8, the word 'it' refers to _______.

A. being too old to learn

B. teaching himself how to play soccer

C. playing for many years

D. looking for a good coach

32. What will the writer probebly do?

A. Teach himself again to play soccer

B. Find a job instead of play soccer

C. ask his friends to teach him soccer

D. Look for a place that teaches adults soccer

1
23 tháng 8 2020

Mark the letter A, B, C or D on your answer sheet to indicate the word whose underlined part differs from the other three in pronunciation in each of the following questions.

1. A. doubt B. suburb C. plumber D. climb

2. A. monthly B. sunbathing C. southern D. weather

Mark the letter A, B, C or D on your answer sheet to indicate the word that differs from the other three in the position of primary stress in each of the following questions.

3. A. efficiency B. profitable C. considerate D. mysterious

4. A. occur B. pollute C. typhoon D. access

1: Ten miles ………. a very long distance for us to walk. A. is B. are C. be D. am 2: There are small……………………….between British and American English. A. differences B. difference C. differently D. different 3: The quality of these recordings .................. not very good. A. be B. are C. am D....
Đọc tiếp

1: Ten miles ………. a very long distance for us to walk.

A. is B. are C. be D. am

2: There are small……………………….between British and American English.

A. differences B. difference C. differently D. different

3: The quality of these recordings .................. not very good.

A. be B. are C. am D. is

4: The number of students in this class …………. limited to thirty.

A. be B. are C. is D. am

5: Not only the air but also the oceans ..................... been polluted seriously.

A. have B. has C. is having D. are having

6: Working in the factory ................... not what children should do

A. be B. is C. are D. have been

7: A large number of students in this school………. . English quite fluently

A. speaks B. is speaking C. has spoken D. speak

8: Bread and butter ………..... what she asks for

A. is B. are C. will be D. have been

9: Neither Daisy nor I …........... glad to do that.

A. am B. has been C. are D. is

10: Some of the milk I bought last night ..................... not fresh anymore.

A. is B. is being C. are D. are

11: The use of credit cards in place of cash ................ increased rapidly in recent years.

A. to have B. have C. has D. having

12: The police ……….. to interview Fred about a robbery.

A. want B. wants C. wanting D. has wanted

13: That you take a computer course …............... very necessary.

A. am B. have been C. are D. is

14: Each of the residents in this community ........... responsible for keeping this park clean.

A. is B. am C. are D. were

15: Anything ........................ better than going to the movies tonight.

A. is B. are C. am D. were

16: What time ......................... the news on TV?

A. is B. am C. are D. were

17: The effects of cigarette smoking ................... been proven to extremely harmful.

A. have B. has C. to have D. having

18: Advertisements on TV .......................becoming more competitive than ever before.

A. is B. are C. was D. was

19: Mr. Thomson with his wife and his three children ............… abroad

A. to be B. have been C. are D. is

20: A pair of jeans .................... in the washing machine this morning.

A. is B. are C. have been D. were

0
Choose from the four options given (marked A, B, C and D) one best answer to complete each sentence 1. Lisa's been able to play the piano since she was six, ____? A. wasn't he B. hasn't she C. isn't she D. has not she 2. The woman felt proud of her husband. She lived next door. A.The woman who living next door felt proud of her husband . B. The woman who lived next door felt proud of her husband . C. The woman who lives next door felt proud of...
Đọc tiếp

Choose from the four options given (marked A, B, C and D) one best answer to complete each sentence

1. Lisa's been able to play the piano since she was six, ____?

A. wasn't he B. hasn't she C. isn't she D. has not she

2. The woman felt proud of her husband. She lived next door.

A.The woman who living next door felt proud of her husband .

B. The woman who lived next door felt proud of her husband .

C. The woman who lives next door felt proud of her husband .

D. The woman lived next door felt proud of her husband .

3. Everybody congratulated the astronauts ____ their successful trip into space.

A. for B. of C. in D. on

4. From the four underlined words or phrases A,B,C, or D, identify the one that is not correct.

Neither James or his brother has been come to Paris.

A B C D

5. Choose the word which has the underlined part pronounced differently from the rest.

A. hoped B. admired C. missed D. looked

6. From the four underlined words or phrases A,B,C, or D, identify the one that is not correct.

This year, that is for the first time, the event is open to all amateur athletes along with the traditional professional.

A B C D

7. ____________ I bought the golden fish.

A. It was from this shop that B. It was this shop which C. It was this shop that D. I was from this shop where

8. Despite the bad weather, he ____ get to the airport in time.

A. couldn't B. can C. was able to D. almost

9. EMS stand for ____.

A. Express Mail Service B. Electronic Mail Service C. Economic Mail Service D. Environment management Service

10. ____________in 2001 that the World Trade Center was destroyed.

A. It was B. What was C. It is D. Which was

11. You should not indulge yourself ____________ anything that can form a bad habit.

A. on B. at C. in D. for

12. He is very good at ____________ people singing with his guitar.

A. accompanying B. making C. having D. getting

13. When the sky is blue and the sun is shining, you may say to your friends "_____"

A. What a beautiful day, is it? B. A beautiful day, is not it?

C. It's not a beautiful day. D.It's a beautiful day, isn't it?

14. Many rare ____ of animals are in danger of extinction.

A. species B. pairs C. beings D. classes

15. I left it ____ on the table ____ in the drawer.

A. neither - or B. either - nor C. either - either D. either - or

1
12 tháng 5 2018

Choose from the four options given (marked A, B, C and D) one best answer to complete each sentence

1. Lisa's been able to play the piano since she was six, ____?

A. wasn't he B. hasn't she C. isn't she D. has not she

2. The woman felt proud of her husband. She lived next door.

A.The woman who living next door felt proud of her husband .

B. The woman who lived next door felt proud of her husband .

C. The woman who lives next door felt proud of her husband .

D. The woman lived next door felt proud of her husband .

3. Everybody congratulated the astronauts ____ their successful trip into space.

A. for B. of C. in D. on

4. From the four underlined words or phrases A,B,C, or D, identify the one that is not correct.

Neither James or=>nor his brother has been come to Paris.

A B C D

5. Choose the word which has the underlined part pronounced differently from the rest.

A. hoped B. admired C. missed D. looked

6. From the four underlined words or phrases A,B,C, or D, identify the one that is not correct.

This year, that is for the first time, the event is open to all amateur athletes along with the traditional professional.

A B C D

7. ____________ I bought the golden fish.

A. It was from this shop that B. It was this shop which C. It was this shop that D. I was from this shop where

8. Despite the bad weather, he ____ get to the airport in time.

A. couldn't B. can C. was able to D. almost

9. EMS stand for ____.

A. Express Mail Service B. Electronic Mail Service C. Economic Mail Service D. Environment management Service

10. ____________in 2001 that the World Trade Center was destroyed.

A. It was B. What was C. It is D. Which was

11. You should not indulge yourself ____________ anything that can form a bad habit.

A. on B. at C. in D. for

12. He is very good at ____________ people singing with his guitar.

A. accompanying B. making C. having D. getting

13. When the sky is blue and the sun is shining, you may say to your friends "_____"

A. What a beautiful day, is it? B. A beautiful day, is not it?

C. It's not a beautiful day. D.It's a beautiful day, isn't it?

14. Many rare ____ of animals are in danger of extinction.

A. species B. pairs C. beings D. classes

15. I left it ____ on the table ____ in the drawer.

A. neither - or B. either - nor C. either - either D. either - or