Mark the letter A, B, C, or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.
The amounts of oxygen and nitrogen in the air almost always remain stable, but the amount of water vapor vary considerably.
A. The amount of
B. almost always
C. stable
D. vary
Đáp án D
- The amount of + N + V chia số ít: số lượng …
ð Đáp án D (vary => varies)