题目内容：

I did not hear the phone,I___asleep.A.must be B.must have been C.should be D.should have been

优质解答

选B
must have been 是对过去的猜测,我没听见电话响,我一定是睡着了.

追问：

那A不行吗？

追答：

A表示对现在的推测，而前一句用的是过去式。