（三）幾組詞的辨異
1. can 和be able to
1）情態(tài)動詞can只有兩種時態(tài)形式，現(xiàn)在式can和過去式could，而be able to有多種時態(tài)形式。
Mary can play the piano. She has been able to play it since she was 5.
瑪麗會彈鋼琴。她五歲起就會彈了。
2）用在過去時中，could經(jīng)常表示能夠做某事，事實上不一定去做，而was∕were able to則表示“過去做成了某事”。在否定句中兩者可通用。
He could swim across the English Channel. But he didn't feel like it that day.
他能游過英吉利海峽，但那天他不想游。
Yesterday I was able to get home before the heavy rain. 昨天我在下大雨前趕到了家里。
2. must和 have to
must表示主觀意志，而have to表示由于客觀因素不得不做某事。must沒有過去式，除在間接引語中可用于表示過去時間，在直接引語中表示過去時間應該用had to代替。
I told her that she must give up smoking. 我叫她必須戒煙。
We had to get everything ready that night. 我們那晚得把一切準備就緒。
3. would和used to
1）used to表示過去與現(xiàn)在或過去某時與后來的情況有不同，而would只表過去的情況。
People used to think that the earth was flat.
過去人們認為地球是平的。（現(xiàn)在人們不這么認為。）
She would go out for a walk in the morning when she was in the country.
在鄉(xiāng)下時，她總是在早晨去散會兒步。（可能現(xiàn)在仍有散步的習慣。）
2）used to可表示過去的習慣動作和經(jīng)常的情況，而would只表示過去的習慣動作。
He used to ∕would smoke while writing. 過去他寫東西時常抽煙。
She used to be fat. 她過去很胖。
1. I __________ you，because I thought I must be wrong.
A. dare not ask B. dare not to ask C. dare not asking D. dare to not ask
2. There __________ some flowers in the garden.
A. were used to be B. used to be C. uses to be D. used to be having
3. “__________ I take it out？” “I'm sorry，you __________.”
A. Could …couldn't B. Might…might not C. Could…can D. May…can't
4. You were stupid to climb the tree. You __________ hurt yourself.
A. may B. might C. will D. might have
5. You __________ those letters. Why didn't you ？
A. should post B. should have posted C. must have posted D. ought to post.
6. All the lights are on，the Smiths __________ up.
A. must get B. is getting C. must be getting D. would get
7. He __________ lead a horse to the water but he __________ not make it drink.
A. will…can B. may…can C. may…dares D. dare…can
8. “Need we do this job now？” “Yes，__________.”
A. you need B. you should C. you must D. you can
9. __________ to have lunch with us today？
A. Do you likes B. Would you like C. Will you liked D. Have you liked
10. He said that you __________ watch TV all the evening if you wished.
A. may B. must C. can D. might
11. –Is John coming by train？ ——He should，but he __________ not. He likes driving his car.
A. must B. can C. need D. may
12. Peter __________ come with us tonight，but he isn't very sure yet.
A. must B. can C. may D. will
13. Michael __________ be a policeman，for he's much too short.
A. needn't B. can't C. shouldn't D. won't 14. I thought you __________ be hungry，so I have brought you some cakes.
A. may B. might C. can D. could
15. I wonder how he __________ that to the teacher.
A. dare to say B. dare saying C. not dare say D. dared say
16. Come on！ We __________ hurry because there isn't much time left.
A. may B. must C. can D. need
17. Amy did best in the English test. She __________ hard last week.
A. must have working B. should have worked C. should work D. must work
18. The fire spread through the hotel very quickly but everyone __________ get out.
A. had to B. would C. could D. was able to
19. ——I stayed at a hotel while in New York. ——Oh，did you？ You __________ with Barbara.
A. could have stayed B. could stay C. would stay D. must have stayed
20. It's nearly seven o'clock. Jack __________ be here at any moment.
A. must B. need C. should D. can
************************************：
1.A2.B3.D4.D5.B6.C7.B8.C9.B10.D11.D12.C13.B14.B15.D16.B17.A18.D19.A20.C
1. can 和be able to
1）情態(tài)動詞can只有兩種時態(tài)形式，現(xiàn)在式can和過去式could，而be able to有多種時態(tài)形式。
Mary can play the piano. She has been able to play it since she was 5.
瑪麗會彈鋼琴。她五歲起就會彈了。
2）用在過去時中，could經(jīng)常表示能夠做某事，事實上不一定去做，而was∕were able to則表示“過去做成了某事”。在否定句中兩者可通用。
He could swim across the English Channel. But he didn't feel like it that day.
他能游過英吉利海峽，但那天他不想游。
Yesterday I was able to get home before the heavy rain. 昨天我在下大雨前趕到了家里。
2. must和 have to
must表示主觀意志，而have to表示由于客觀因素不得不做某事。must沒有過去式，除在間接引語中可用于表示過去時間，在直接引語中表示過去時間應該用had to代替。
I told her that she must give up smoking. 我叫她必須戒煙。
We had to get everything ready that night. 我們那晚得把一切準備就緒。
3. would和used to
1）used to表示過去與現(xiàn)在或過去某時與后來的情況有不同，而would只表過去的情況。
People used to think that the earth was flat.
過去人們認為地球是平的。（現(xiàn)在人們不這么認為。）
She would go out for a walk in the morning when she was in the country.
在鄉(xiāng)下時，她總是在早晨去散會兒步。（可能現(xiàn)在仍有散步的習慣。）
2）used to可表示過去的習慣動作和經(jīng)常的情況，而would只表示過去的習慣動作。
He used to ∕would smoke while writing. 過去他寫東西時常抽煙。
She used to be fat. 她過去很胖。
1. I __________ you，because I thought I must be wrong.
A. dare not ask B. dare not to ask C. dare not asking D. dare to not ask
2. There __________ some flowers in the garden.
A. were used to be B. used to be C. uses to be D. used to be having
3. “__________ I take it out？” “I'm sorry，you __________.”
A. Could …couldn't B. Might…might not C. Could…can D. May…can't
4. You were stupid to climb the tree. You __________ hurt yourself.
A. may B. might C. will D. might have
5. You __________ those letters. Why didn't you ？
A. should post B. should have posted C. must have posted D. ought to post.
6. All the lights are on，the Smiths __________ up.
A. must get B. is getting C. must be getting D. would get
7. He __________ lead a horse to the water but he __________ not make it drink.
A. will…can B. may…can C. may…dares D. dare…can
8. “Need we do this job now？” “Yes，__________.”
A. you need B. you should C. you must D. you can
9. __________ to have lunch with us today？
A. Do you likes B. Would you like C. Will you liked D. Have you liked
10. He said that you __________ watch TV all the evening if you wished.
A. may B. must C. can D. might
11. –Is John coming by train？ ——He should，but he __________ not. He likes driving his car.
A. must B. can C. need D. may
12. Peter __________ come with us tonight，but he isn't very sure yet.
A. must B. can C. may D. will
13. Michael __________ be a policeman，for he's much too short.
A. needn't B. can't C. shouldn't D. won't 14. I thought you __________ be hungry，so I have brought you some cakes.
A. may B. might C. can D. could
15. I wonder how he __________ that to the teacher.
A. dare to say B. dare saying C. not dare say D. dared say
16. Come on！ We __________ hurry because there isn't much time left.
A. may B. must C. can D. need
17. Amy did best in the English test. She __________ hard last week.
A. must have working B. should have worked C. should work D. must work
18. The fire spread through the hotel very quickly but everyone __________ get out.
A. had to B. would C. could D. was able to
19. ——I stayed at a hotel while in New York. ——Oh，did you？ You __________ with Barbara.
A. could have stayed B. could stay C. would stay D. must have stayed
20. It's nearly seven o'clock. Jack __________ be here at any moment.
A. must B. need C. should D. can
************************************：
1.A2.B3.D4.D5.B6.C7.B8.C9.B10.D11.D12.C13.B14.B15.D16.B17.A18.D19.A20.C