Câu hỏi: Exactly .............. we can replace our soil disappearing through erosion is not known.

A. what

B. how

C. if

D. because

Câu 1: A small design fault ................. on our latest chip.

A. has found

B. found

C. has been found 

D. find

Câu 2: If it ..................... last weekend, we would have gone skiing.

A. snowed

B. would have snowed

C. had snowed

D. would snow

Câu 3: We’ll have to break the ice on the pond; otherwise the ducks .............. swim.

A. are not able to

B. will not be able to

C. would not be able to

D. would not have been able to

Câu 4: If you ................... a pet bird, you’ll have to buy a cage, too.

A. buy

B. will buy

C. bought

D. had bought

Câu 5: If it ............................... his wife’s money, he’d never be a director.

A. was

B. isn’t 

C. had had

D. were not for

Câu 6: Hamburgers ...................... favorite in America in the early century.

A. became

B. becomes

C. has become

D. was become