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：否定回答可用can ,mustn 或may not，may not 可能不，can 不能够，mustn 一定不，禁止；be allowed to被允许做某事；be supposed to应该，被期望做某事；句意：我们现在可以离开教室吗？不，你们不能。你们直到铃响才能离开教室。结合语境可知前文用can’t，mustn’t语气较重，may not语气太轻。同理，be allowed to语气则太重，故选D，为最佳答案。
