情态动词表推测时,该句的反义疑问句和情态动词无关,必须去掉该情态动词后,考虑句子谓语动词的发生时间和谓语构成,再进行相应的变化.
如：
1.It must have rained last night,didn't it?
去掉must后,考虑时间状语last night,说明句子本该使用一般过去时,即变成：It rained last night,所以其反义疑问句为didn't it?
再如：
2.You can't have been to Beijing before,have you?
去掉can't后,根据句意,句子本该使用现在完成时,即变成：You haven't been to Beijing before,所以其反义疑问句为have you?