It's necessary __________ the car when you do not use it.
| A．of you to lock | B．for you locking |
| C．for you to lock | D．for you to be locked |
I’m sorry to have kept you ________ for a long time.
A. wait b. to wait c. waiting D. to be waiting
The film __________ for ten minutes when we got to the cinema.
| A． had already been on | B．had already begun |
| C．have already been on | D．have already begun |
Three years ____ a long time for us students.
| A．are | B．be | C．is | D．have been |
To a doctor, the most important thing is _______.
A. to save b. saving C. to saving D. saved
Can you tell me ________?
| A．what are they doing that for | B．why they are doing for |
| C．why are they doing that | D．what they are doing that for |