Why didn't you answer the telephone last night?
问题描述：
Why didn't you answer the telephone last night?
I did't hear the phone .I ___
A:must be asleep
B;must have been asleep
A为什么不选啊
答
选择B,这是一个过去完成时表示的状态,表示asleep这一状态是过去的,并且是已经完成的,“我那时一定睡着了” ,如果用A,意思就是“我一定睡着了”,没有过去的意思,与问话不符,倒不如说I was asleep.