2020年上半年英语四级真题_2020年上半年英语四级语法知识整理

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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。

表示推测的用法

　　can, could, may, might, must 皆可表示推测，其用法如下：

　　1)情态动词+动词原形。

　　表示对现在或将来的情况的推测，此时动词通常为系动词。

　　I don't know where she is, she may be in Wuhan.

　　2)情态动词+动词现在进行时。

　　表示对现在或将来正在进行的情况进行推测。

　　At this moment, our teacher must be correcting our exam papers.

　　这时，我们老师想必在批改试卷。

　　3)情态动词+动词完成时。

　　表示对过去情况的推测。

　　We would have finished this work by the end of next December.

　　明年十二月底前我们很可能已完成这项工作了。

　　The road is wet. It must have rained last night.

　　地是湿的，昨天晚上一定下雨了。

　　4)情态动词+动词的现在完成进行时。

　　表示对过去正在发生事情的推测。

　　Your mother must have been looking for you.

　　你 妈妈一定一直在找你。

　　5)推测的否定形式，疑问形式用can't, couldn't表示。

　　Mike can't have found his car, for he came to work by bus this morning.

　　迈克一定还没有找回他的车，因为早上他是坐公共汽车来上班的。

　　注意：could, might表示推测时不表示时态，其推测的程度不如can, may。

情态动词+ have +过去分词

　　1) may(might) have + done sth, can (could) have + done sth　表示过去，推测过去时间里可能发生的事情。

　　Philip may (might) have been hurt seriously in the car accident.

　　Philip can (could) have been hurt seriously in the car accident.

　　2)　must have +done sth，对过去时间里可能发生的事情的推测，语气较强，具有"肯定"，"谅必"的意思。

　　---Linda has gone to work, but her bicycle is still here.

　　---She must have gone by bus.

　　3) ought to have done sth, should have done sth

　　本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。

　　You ought to (should) have been more careful in this experiment.

　　He ought not to have thrown the old clothes away.(事实上已扔了。)

　　ought to 在语气上比should 要强。

　　4) needn't have done sth　 本没必要做某事

　　I dressed very warmly for the trip, but I　needn't have done so. The weather was hot.

　　5) would like to have done sth　 本打算做某事

　　I would like to have read the article, but I was very busy then.

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