When I try to find _______ that prevents so many people from taking part in the program,it seems to me that there are two main causes.
| A．why it does | B．what it does |
| C．what it is | D．why it is |
The police still haven’t found her, but they’re doing all they _____.
| A．may | B．can | C．must | D．will |
The World Wide Web is sometimes jokingly called the World Wide Wait because it _________be very slow.
| A．should | B．must | C．will | D．can |
—The woman biologist stayed in Africa studying wild animals for 13 years before she returned.
— Oh, dear! She _________ a lot of difficulties!
| A．may go through | B．might go through |
| C．ought to have gone through | D．must have gone through |
—Lucy doesn’t mind lending you her dictionary.
—She _________. I’ve already borrowed one.
| A．can’t | B．mustn’t | C．needn’t | D．shouldn’t |
—I’ve taken someone else’s green sweater by mistake.
—It _________ Harry’s. He always wears green.
| A．has to be | B．will be | C．mustn’t be | D．could be |