1. When I ___________ the knock, I ______ the door.

A. was hearing/ opened         B. heard/ opened         

 C. was hearing/ was opening        D. heard/ have opened 

2. He ______ able to drive since he had an accident 5 years ago .

A. has not been                B. will not be 

C. had not been               D. would not be

3. We __ for months before we reached an island

.A. have been sailing                   B. had been sailing

C. would be sailing                     D. were sailing

4. They ____ the trip until we come. 

A. will start            B. didn’t start          C. started            D. won’t start
giúp em vs ạ