自考英语语法复习资料(26)

（三）几组词的辨异

1. can 和be able to

1）情态动词can只有两种时态形式，现在式can和过去式could，而be able to有多种时态形式。

Mary can play the piano. She has been able to play it since she was 5.

玛丽会弹钢琴。她五岁起就会弹了。

2）用在过去时中，could经常表示能够做某事，事实上不一定去做，而was∕were able to则表示“过去做成了某事”。在否定句中两者可通用。

He could swim across the English Channel. But he didn't feel like it that day.

他能游过英吉利海峡，但那天他不想游。

Yesterday I was able to get home before the heavy rain. 昨天我在下大雨前赶到了家里。

2. must和 have to

must表示主观意志，而have to表示由于客观因素不得不做某事。must没有过去式，除在间接引语中可用于表示过去时间，在直接引语中表示过去时间应该用had to代替。

I told her that she must give up smoking. 我叫她必须戒烟。

We had to get everything ready that night. 我们那晚得把一切准备就绪。

3. would和used to

1）used to表示过去与现在或过去某时与后来的情况有不同，而would只表过去的情况。

People used to think that the earth was flat.

过去人们认为地球是平的。（现在人们不这么认为。）

She would go out for a walk in the morning when she was in the country.

在乡下时，她总是在早晨去散会儿步。（可能现在仍有散步的习惯。）

2）used to可表示过去的习惯动作和经常的情况，而would只表示过去的习惯动作。

He used to ∕would smoke while writing. 过去他写东西时常抽烟。

She used to be fat. 她过去很胖。

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