The light went out,so Mary must have gone to sleep,________?

The light went out,so Mary must have gone to sleep,________?
答案为A.
此题句意为：灯关了,玛丽肯定已经睡觉了.这是一个对过去情况的推测,所以,其反义疑问句的第二部分应该用一般过去时.
情态动词表推测的反义问疑句比较特殊,他们的反义部分不用情态动词,而要与第一部分中的动词种类相应一致.
如：Judging from his looks,he might/ may/ must be happy,isn’t he?
I meet him here almost every day,and he might/ may/ must live nearby,doesn’t he?
Two of them were absent yesterday,and they might/ may/ must have fallen ill,didn’t they?(此句是对过去情况的推测)
Two of them are absent today,and they might/ may/ must have fallen ill,haven’t they?
(此句是对现在情况的推测)
欢迎提问,