巧记must-can-may表示“推测”的用法.doc

巧记must, can, may表示“推测”的用法
首先请看下面的顺口溜：can不肯，may不问，must肯定不否问。
这个顺口溜介绍了can (could), may (might), must 表“推测”时所适用的句式的区别。其含义如下：
can不肯，即：can (could) 一般不用于肯定句；may不问，即：may (might)　一般不用于疑问句；must肯定不否问，即：must一般仅用于肯定句，不用于否定句和疑问句。
一、表示有把握的推测时，肯定句用must (一定，准是)，否定句用can’t (不可能，一定不)。must(can’t) + 动词原形，表示对现在情况的推测。must(can’t) + be doing, 表示对现在正在进行的情况的推测。must(can’t) + have done，表示对过去情况的推测。例如：
You must be hungry after a long walk.
长途步行之后你一定饿了。
They must be waiting for us. Let’s hurry up.
他们一定在等我们。让我们快点走吧。
You must have left your bag in the theatre.
你准是把你的包丢在剧院了。
You can’t be hungry, you have just had your dinner.
你现在不可能觉得饿，你刚吃过饭。
He wears glasses all the time, his eyesight can’t be getting better.
他一直带着眼镜，他的视力不可能在好转。
He has no idea what the book is about, he can’t have read it very carefully.
他一点也不知道这本书是关于什么的，他一定没有仔细读过此书。
二、表示把握不大的推测即可能性时，用can和may，常译为“也许，可能”。may用于肯定句与否定句，一般不用于疑问句。can常用于疑问句，一般不用于肯定句。例如：
The news may or may not be true.
这消息也许是真的，也许不是真的。
At the moment she may be playing with her classmates.
此刻她可能正在和同学们玩。
Anna might not have seen Tom yesterday.
安哪昨天可能没有看见汤姆。
Where can Wei Fang be?
魏芳会在哪里呢？
What can they be quarrelling about?
他们可能在争吵些什么呢？
Can she have lost the book?
她可能已把那本书丢了？

跟踪小练习：
从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
1． Jenny ______ with him at that time, for I was having dinner with her in my home.
A. can’t have been     B. mustn’t have been   
C. must have been       D. may have been
2. It is cold in the room. They ______ have turned off the heating.
A. must      B. ought to       C. should      D. could
3. — Someone is knocking at the door.
— Who ______ it be at this hour of day?
A. may       B. can        C. must       D. should
4. I didn’t hear the phone. I ______ asleep.
A. must be             B. must have been 
C. should be           D. should have been
5. Johnson ______ be a policeman. He is much too short.
A. may      B. mustn’t        C. should      D. can’t
6. — Jack fell off a ladder yesterday, but he was all right.
— He is lucky. He ______ himself badly.
A. can have hurt        B. could have wounded 
C. might have hurt      D. must have wounded
7. — Who told you the news?
— I don’t remember clearly. It ______ Mary.
— It ______ Mary. She doesn’t know it.
A. may have been; can’t be       
B. can be; mustn’t be  
C. must have been; can’t have been  
D. may have been; may not be

Key: 1. A  2. A  3. B  4. B  5. D  6. C  7. A