句式 说明 例句
can +不定式完成式 表示“可能”，用于否定句和疑问句（could 也可能有此用法，只是语气更委婉） He can’t be telling lies.
He can’t have told lies.
could+不定式完成式 指过去没实现的动作，表“本来可以” It’s too late. You could have told him earlier.你本来能早点告诉他的。
may+不定式完成式 表示“可能，也许”，用于肯定句 He may be doing homework.
He may have missed the train.
语法易错题must+不定式进行式 肯定句表示“一定在干某事”The light is on. He must be working.灯亮着，他一定在工作。must+不定式完成式 用于肯定句，表示“准是干了某事” He is sad. He must have failed the exam.他准是考试不及格。needn’t+不定式完成式 “本来不必做”，只用于否定句 You needn’t have lent the book to him. He bought it already.你本来不必把这本书借给她，他已经买了一本。should/ought to+不定式完成式 肯定句表示“本应该做而实际没做”；否定句表示“不应该做而实际却做了” I should have bought it.我应该把它买下来的。You shouldn’t have scolded him.你不应该这样粗心大意。填入情态动词的恰当形式或根据括号所提供的词填入情态动词恰当的结构。1. I should have been there, but I ____________ find the time.2. Helen _______ go on the trip with us, but she isn’t quite sure yet.3. Tom, you ___________ not leave all your clothes on the floor like this!4. You can’t imagine that a well behaved gentleman _____________ be so rude to a lady.5. It has been announced that candidates_____________ remain in their seats until all the papers have been collected.6. ---Lucy doesn’t mind lending you her dictionary.---She ____________. I’ve already borrowed one.7. John, look at the time. _______________ you play the piano at such a late hour?8. ---__________ this book be yours?---No, it ____________ not be mine. It ___________ be his.9. As a girl, she ____________ get up at six every day.10. __________ he to clean the classroom after school?11. You ____________ be tired after the long trip, aren’t you?12. ---What’s the name?---Khulaifi. __________ I spell that for you?13. You _____________________ (see) the film, haven’t you?14. You _____________________ (talk) on the phone at that time, for I couldn’t get through.15. They _____________________ (miss) the plane, or perhaps they have been prevented from coming for some reason.16. ______________ you pass the college entrance examinations!17. He had known the matter before you told him, so you _____________________ (not tell) it to him.18. I did not call to make any airline reservation but I ________________.19. The light is out. They _______________________ (not work) now.20. ---My cat is really fat.---You _____________________ (not give) her so much food.答案：1. couldn’t 2. may 3. mustn’t 4. should 5. shall 6. needn’t 7. Must 8. Can; can’t; must 9. would 10. Ought 11. must 12. shall 13.must have seen 14. must be talking 15. might/might have missed 16. May 17. needn’t have told 18. should have 19. can’t be working 20. shouldn’t have given