问题补充：
-May we leave the classroom now?
-No, you . You to leave until the bell rings.
A. mustn’t, are allowed
B. don’t have to, are supposed
C. needn’t, aren’t allowed
D. can’t, aren’t supposed
答案：
A. mustn’t, are allowed
B. don’t have to, are supposed
C. needn’t, aren’t allowed
(答案→)D. can’t, aren’t supposed
解析：考察情态动词否定回答及allow和suppose用法. mustn’t,禁止don’t have to, 不必needn’t,不必can’t不能.be supposed to应该,被期望做某事,be allowed to do sth 被允许做某事.根据题意,我们现在可以离开房间了吗？——不，你们不能。你们铃响之前别想 离开。选D。
