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must表示推测 的用法

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must表示推测 的用法
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.