(一)情態(tài)動詞無人稱和數(shù)的變化，其后可跟不定式的一般式，也可跟不定式的完成式。can用在否定句中，表示否定的判斷或推測以及理論上的可能性，其肯定形式為must+原形;could+原形動詞表示現(xiàn)在或將來的推測或判斷。
That can’t be true.
It must be done.
You could be right.
(二)can和could可用于下列結構：
can’t help + v-ing
cannot help but不得不
can but只得
cannot choose but只得
cannot…too (over)無論……也不過分
One cannot be too careful.
I can but say it again.
(三)can或could與不定式的完成式連用，表示說話人對過去發(fā)生的行為的真實性所持的態(tài)度(驚奇或懷疑)。can只用于疑問句或否定句。can’t/ couldn’t have + 過去分詞表示對過去情況的強烈否定推測，一般譯為“一定沒……”。
Where can she have gone?
She can’t have gone to school. — It’s Sunday.
He could have gone off with some friends.
(四)may和might均可表示可能性和許可。may可表示給予許可，might則不能。may用于現(xiàn)在和將來時，might用于過去時或表示婉轉意義，或可能性不大。
She may not be at home. (= It is possible that she is not at home.)
She can’t be at home. (= it is not possible that she is at home.)
Brown might come to sign up for the match 2 days later.
(五)may +不定式的完成式表示說話人對過去發(fā)生的事情的懷疑與推測;might+不定式的完成式表示對過去發(fā)生的事情可能性的推測，所推測的可能性有時與實際情況相反，一般含批評、責備的口吻?？赡苄宰钚 ?BR> She is late. She may have got up late.
You might have done it better.
(六)must表示義務時，其否定式形式為don’t need to, needn’t + V或don’t have to.
You needn’t come to see me if you don’t want to.
You don’t have to talk so loud.
(七)must + 不定式的完成式表示對過去發(fā)生的事情較有把握的推測，譯為“一定……”，否定式為can’t have done.
The road is wet. It must have rained last night.
He can’t have finished all the exercises within an hour.
(八)ought to 與should + 不定式的完成式用于肯定句，表示該做而未做，用于否定句表示不該做的事而做了，有強烈的批評與責備口吻。
You ought to have handed in your homework this morning.
You should not have done such a foolish thing.
(九)needn’t have + 過去分詞表示做了不必做的事，譯為“其實沒有必要……”。
You have five days more. You needn’t have worked so hard.
Exercise 3.1
1. The film was wonderful; you ______ it.
A. must go to see
B. must have gone to see
C. should have gone to see
D. may see
2. “We didn’t see him at the lecture yesterday.”
“He ______ it.”
A. mustn’t attend
B. can’t have attended
C. should not have attended
D. needn’t have attended
3. The elephants ought ______ hours ago by the keepers.
A. to be fed B. to feed
C. to being fed D. to have been fed
4. She went to sleep in the park and when she woke up her watch had vanished. Someone ______ it while she slept.
A. must steal
B. should have stolen
C. must have stolen
D. need have stolen
5. If you ______ over there for a moment, I’ll tell Mr. Li you’ve arrived.
A. shall wait B. waited
C. will wait D. should wait
6. The room is in a terrible mess. It ______ cleaned
A. mustn’t be
B. mustn’t have been
C. can’t be
D. can’t have been
7. In the eighteenth century writers ______ hours in coffee houses, discussing the news of the day.
A. may spend B. would spend
C. might have spent D. could spend
8. I wish that I ______ with you last night.
A. went B. have gone
C. could go D. could have gone
9. He was a good runner so he ______ escape from the police.
A. ought to B. might
C. was able to D. could
10. “Have you seen Marie?”
“She wasn’t feeling well. ______ gone home?”
A. She might have B. She might has
C. Might she have D. She could have
11. If the telephone ______ ring please say that I’ll be back at six.
A. should B. will
C. shall D. can
12. “You ought to have gone to see your uncle yesterday.” “Yes, I ______.”
A. should B. ought to
C. would to D. should have
13. Nobody knows how people first came to these islands. They ______ from South America on rafts.
A. must have sailed B. can sail
C. might have sailed D. should have sailed
14. “I don’t know what has happened to Harold,” she said.
“Maybe I ______ him.”
A. had to call B. shall call
C. should call D. would call
15. “What did Pat do last night?”
“She ______ tickets to a football game, but decided to stay home.”
A. could get B. could has gotten
C. could have gotten D. can get
16. You are incompetent! It ______ hours ago.
A. should be finished
B. must be finished
C. must have finished
D. should have been finished
17. “Can we finish cleaning this garage tonight?”
“I don’t know, but we ______ try to.”
A. would B. used to
C. should D. were able to
18. “Helen, will you be at the party tonight?”
“I don’t know, because I have so much homework to do that I really ______.”
A. can’t B. mustn’t
C. won’t D. shouldn’t
19. “I didn’t go to class last night because my car broke down.”
“You ______ mine. I wasn’t using it.”
A. could borrow
B. could have borrowed
C. may have borrowed
D. may borrow
20. To be really happy and safe, one ______ at least two or three hobbies, and they must all be real.
A. would have B. could have
C. ought to have D. may have
Exercise 3.2
1. Professor Wang left for London yesterday. He _____ be in his home London now.
A. might B. may not
C. dare D. need
2. _____ your sister have caught up with them?
A. May B. should
C. Might D. Will
3. Tom _____ break in like that.
A. ought to not B. ought not to
C. not ought to D. ought
7. The classroom _____ be cleaned before the class begins.
A. needs t B. needs
C. need to D. needs not
8. They _____ go out right now. these are still one hour left.
A. don’t need B. doesn’t need
C. needs to D. don’t need to
9. The man shouted at them crazily and they _____ look at him.
A. dare B. don’t dare
C. dare not D. not dare
10. _____ you pick up the burning iron with your bare hands?
A. Daren’t to B. Dare
C. Do dare D. Dared
11. Peter _____ get near to the dog, for he is only a schoolboy.
A. doesn’t dare B. dares not
C. dare not to D. doesn’t dare to
12. Nobody _____ walk over the bridge at night.
A. dares B. dared not
C. dared to D. don’t dare to
13. _____ you _____ school by bus?
A. Used…to B. Used… to go
C. Used…go D. Used…to going
14. You _____ not to make fun of him. He is not the one you laugh at but learn from.
A. should B. ought
C. had better D. shall
15. You’d _____ laugh in this kind of ceremony.
A. better laugh not B. better to
C. better not D. not bette
16. Linda _____ it down. She was here yesterday.
A. couldn’t B. couldn’t knock
C. could knock D. could have knocked
17. It was dark there. They _____ their way.
A. must have been B. must have lost
C. may lose D. must lose
18. They went to the classroom a moment ago. They _____ class in the classroom right now.
A. must have to B. could have
C. may have had D. might be having
19. I _____ have told you all these, but I didn’t.
A. could B. would
C. ought D. should
20. We have several days more. We _____ worked so hard.
A. needn’t have B. couldn’t have
C. mustn’t have D. needn’t
That can’t be true.
It must be done.
You could be right.
(二)can和could可用于下列結構：
can’t help + v-ing
cannot help but不得不
can but只得
cannot choose but只得
cannot…too (over)無論……也不過分
One cannot be too careful.
I can but say it again.
(三)can或could與不定式的完成式連用，表示說話人對過去發(fā)生的行為的真實性所持的態(tài)度(驚奇或懷疑)。can只用于疑問句或否定句。can’t/ couldn’t have + 過去分詞表示對過去情況的強烈否定推測，一般譯為“一定沒……”。
Where can she have gone?
She can’t have gone to school. — It’s Sunday.
He could have gone off with some friends.
(四)may和might均可表示可能性和許可。may可表示給予許可，might則不能。may用于現(xiàn)在和將來時，might用于過去時或表示婉轉意義，或可能性不大。
She may not be at home. (= It is possible that she is not at home.)
She can’t be at home. (= it is not possible that she is at home.)
Brown might come to sign up for the match 2 days later.
(五)may +不定式的完成式表示說話人對過去發(fā)生的事情的懷疑與推測;might+不定式的完成式表示對過去發(fā)生的事情可能性的推測，所推測的可能性有時與實際情況相反，一般含批評、責備的口吻?？赡苄宰钚 ?BR> She is late. She may have got up late.
You might have done it better.
(六)must表示義務時，其否定式形式為don’t need to, needn’t + V或don’t have to.
You needn’t come to see me if you don’t want to.
You don’t have to talk so loud.
(七)must + 不定式的完成式表示對過去發(fā)生的事情較有把握的推測，譯為“一定……”，否定式為can’t have done.
The road is wet. It must have rained last night.
He can’t have finished all the exercises within an hour.
(八)ought to 與should + 不定式的完成式用于肯定句，表示該做而未做，用于否定句表示不該做的事而做了，有強烈的批評與責備口吻。
You ought to have handed in your homework this morning.
You should not have done such a foolish thing.
(九)needn’t have + 過去分詞表示做了不必做的事，譯為“其實沒有必要……”。
You have five days more. You needn’t have worked so hard.
Exercise 3.1
1. The film was wonderful; you ______ it.
A. must go to see
B. must have gone to see
C. should have gone to see
D. may see
2. “We didn’t see him at the lecture yesterday.”
“He ______ it.”
A. mustn’t attend
B. can’t have attended
C. should not have attended
D. needn’t have attended
3. The elephants ought ______ hours ago by the keepers.
A. to be fed B. to feed
C. to being fed D. to have been fed
4. She went to sleep in the park and when she woke up her watch had vanished. Someone ______ it while she slept.
A. must steal
B. should have stolen
C. must have stolen
D. need have stolen
5. If you ______ over there for a moment, I’ll tell Mr. Li you’ve arrived.
A. shall wait B. waited
C. will wait D. should wait
6. The room is in a terrible mess. It ______ cleaned
A. mustn’t be
B. mustn’t have been
C. can’t be
D. can’t have been
7. In the eighteenth century writers ______ hours in coffee houses, discussing the news of the day.
A. may spend B. would spend
C. might have spent D. could spend
8. I wish that I ______ with you last night.
A. went B. have gone
C. could go D. could have gone
9. He was a good runner so he ______ escape from the police.
A. ought to B. might
C. was able to D. could
10. “Have you seen Marie?”
“She wasn’t feeling well. ______ gone home?”
A. She might have B. She might has
C. Might she have D. She could have
11. If the telephone ______ ring please say that I’ll be back at six.
A. should B. will
C. shall D. can
12. “You ought to have gone to see your uncle yesterday.” “Yes, I ______.”
A. should B. ought to
C. would to D. should have
13. Nobody knows how people first came to these islands. They ______ from South America on rafts.
A. must have sailed B. can sail
C. might have sailed D. should have sailed
14. “I don’t know what has happened to Harold,” she said.
“Maybe I ______ him.”
A. had to call B. shall call
C. should call D. would call
15. “What did Pat do last night?”
“She ______ tickets to a football game, but decided to stay home.”
A. could get B. could has gotten
C. could have gotten D. can get
16. You are incompetent! It ______ hours ago.
A. should be finished
B. must be finished
C. must have finished
D. should have been finished
17. “Can we finish cleaning this garage tonight?”
“I don’t know, but we ______ try to.”
A. would B. used to
C. should D. were able to
18. “Helen, will you be at the party tonight?”
“I don’t know, because I have so much homework to do that I really ______.”
A. can’t B. mustn’t
C. won’t D. shouldn’t
19. “I didn’t go to class last night because my car broke down.”
“You ______ mine. I wasn’t using it.”
A. could borrow
B. could have borrowed
C. may have borrowed
D. may borrow
20. To be really happy and safe, one ______ at least two or three hobbies, and they must all be real.
A. would have B. could have
C. ought to have D. may have
Exercise 3.2
1. Professor Wang left for London yesterday. He _____ be in his home London now.
A. might B. may not
C. dare D. need
2. _____ your sister have caught up with them?
A. May B. should
C. Might D. Will
3. Tom _____ break in like that.
A. ought to not B. ought not to
C. not ought to D. ought
7. The classroom _____ be cleaned before the class begins.
A. needs t B. needs
C. need to D. needs not
8. They _____ go out right now. these are still one hour left.
A. don’t need B. doesn’t need
C. needs to D. don’t need to
9. The man shouted at them crazily and they _____ look at him.
A. dare B. don’t dare
C. dare not D. not dare
10. _____ you pick up the burning iron with your bare hands?
A. Daren’t to B. Dare
C. Do dare D. Dared
11. Peter _____ get near to the dog, for he is only a schoolboy.
A. doesn’t dare B. dares not
C. dare not to D. doesn’t dare to
12. Nobody _____ walk over the bridge at night.
A. dares B. dared not
C. dared to D. don’t dare to
13. _____ you _____ school by bus?
A. Used…to B. Used… to go
C. Used…go D. Used…to going
14. You _____ not to make fun of him. He is not the one you laugh at but learn from.
A. should B. ought
C. had better D. shall
15. You’d _____ laugh in this kind of ceremony.
A. better laugh not B. better to
C. better not D. not bette
16. Linda _____ it down. She was here yesterday.
A. couldn’t B. couldn’t knock
C. could knock D. could have knocked
17. It was dark there. They _____ their way.
A. must have been B. must have lost
C. may lose D. must lose
18. They went to the classroom a moment ago. They _____ class in the classroom right now.
A. must have to B. could have
C. may have had D. might be having
19. I _____ have told you all these, but I didn’t.
A. could B. would
C. ought D. should
20. We have several days more. We _____ worked so hard.
A. needn’t have B. couldn’t have
C. mustn’t have D. needn’t