Câu hỏi: Proteins are made up of folded irregularly chains, the links of which are amino acids.

A. made up of

B. folded irregularly

C. the links

D. which

Câu 1: Although most species of small birds gather in groups at feeders provided by bird-watchers, the bright red cardinals usually appears alone or with its mate.

A. at

B. cardinals

C. or

D. its

Câu 2: The world is becoming more industrialized and the number of animal species that have become extinct have increased.

A. industrialized

B. species

C. extinct 

D. have

Câu 3: The number of students attending universities to study economics have increased steadily in the last few years.

A. of students

B. attending

C. economics

D. have

Câu 4: My elder sisters, both of them were doctors, said they were too busy to pick me up.

A. elder

B. both of them

C. too busy 

D. to pick

Câu 5: Henry David Thoreau was an American writer who is remembered for his faith in religious significance of the nature.

A. an

B. is

C. for

D. the nature

Câu 6: If they took their language lesson seriously, they would be able to communicate with the locals now.

A. took

B. seriously

C.  would be

D. with the locals