Although the causes of cancer_____, we do not yet have any practical way to prevent it.
| A．are being uncovered | B．have been uncovering |
| C．are uncovering | D．have uncovered |
When I was young, I was told that I ______ play with matches
| A．wouldn't | B．needn't | C．mustn't | D．daren't |
-What sort of house do you want to have? Something big?
--Well, it ______ be big--that's not important.
| A．mustn't | B．needn't | C．can't | D．won't |
Although this ____ sound like a simple task, great care is needed.
| A．must | B．may | C．shall | D．should |
—She looks very happy. She ______ have passed the exam.
—I guess so. It’s not difficult after all.
| A．should | B．could | C．must | D．might |
Thank you for all your hard work last week. I don’t think we ______ it without you.
| A．can manage | B．could have managed |
| C．could manage | D．can have managed |