The desk is not dirty．You ________ clean it．
A. mustn’t
B. shouldn’t
C. needn’t
D. can’t
— Can I go to the movie, Mum?
— Certainly. But you _______ be back by ten o’clock.
A. can B. may C. might D. must
Trees ____ fight air pollution．They are natural air conditioners．
A. should B. must C. need D. can
It doesn't look like rain, so you_______ bring your umbrella with you.
A. shouldn't B. mustn't C. can't D. needn't
——Must I leave the room now?
——No，you .
A. needn’t B. can’t C. mustn’t D. couldn’t
——Who’s that man? Is he Mr. Brown?
——That be Mr. Brown. He never walks this way.
A.can’t B. mustn’t C. must D.can
