I didn’t hear the phone. I_______asleep.
A、must be
B、must have been
C、should be
D、should have been
【正确答案】：B
【题目解析】：句意表示对过去所发生过的事情的推测。表示对过去的虚拟/猜测用could/might/must/should/would have done. 由于前面已经说明I didn't hear the phone（我没听到电话响），所以这里的语气应该是比较肯定，所以选must have been.
