Câu hỏi: After the police had tried unsuccessfully to determine to who the car belonged, they towed it to the station.

A. the police

B. unsuccessfully

C. who

D. it to

Câu 1: Each of the beautiful cars in the shop was quickly sold to their owner.

A. Each

B. cars

C. quickly

D. their

Câu 2: It is vitally important that she takes this medication night and morning.

A. vitally

B. that

C. takes

D. medication

Câu 3: By the time Robert will finish writing the first draft of his paper, most of the other students will have completed their final draft.

A. will finish

B. writing

C. most

D. their

Câu 4: For thousands of years, man has created sweet-smelling substances from wood, herbs and flowers and using them for perfumes or medicine.

A. man

B. sweet-smelling

C. using them

D. or

Câu 5: What we know about certain diseases are still not sufficient to prevent them from spreading easily among the population.

A. What we know

B. are

C. from spreading

D. among

Câu 6: Developing new technologies are time-consuming and expensive.

A. developing 

B. technologies

C. are

D. time-consuming