Câu hỏi: How long have they been working _____________ the company?

A. for

B. at

C. in

D. on

Câu 1: A sign warned motorists ______ dangers.

A. of

B. for

C. about

D. a and c

Câu 2: The pens made___________ plastic are very cheap.

A. by

B. with

C. of

D. to

Câu 3: It was very nice__________ him to give me a lift.

A. of

B. by

C. to

D. on

Câu 4: He insisted ______ taking us dinner.

A. on

B. in

C. over

D. of

Câu 5: We congratulate you ___________ your successful flight.

A. on

B. about

C. by

D. with

Câu 6: China became the third country in the world to be able to independently carry __________ manned space flights.

A. by

B. up

C. on

D. out