21.5 must表示推测
1)must用在肯定句中表示较有把握的推测,意为"一定"。
2)must表对现在的状态或现在正发生的事情的推测时,must 后面通常接系动词be 的原形或行为动词的进行式。
You have worked hard all day.You must be tired.你辛苦干一整天,一定累了。(对现在情况的推测判断)
He must be working in his office.他一定在办公室工作呢。
比较:
He must be staying there.他现在肯定呆在那里。
He must stay there.他必须呆在那。
3)must 表示对已发生的事情的推测时,must 要接完成式。
I didn't hear the phone.I must have been asleep.我刚才没有听到电话,我想必是睡着了。
4)must表示对过去某时正发生的事情的推测,must 后面要接不定式的完成进行式。
—Why didn't you answer my phone call?
—Well,I must have been sleeping,so I didn't hear it.
5)否定推测用can't。
If Tom didn't leave here until five o'clock,he can't be home yet.如果汤姆五点才离开这儿,他此时一定还未到家。