情态动词

一、 can, (could 过去式）

1) 表示能力（体力、知识、技能）。

Can you lift this heavy box?（体力）

Mary can speak three languages.（知识）

Can you skate?（技能）

Can只有一般现在时和一般过去式；

2) 表示请求和允许。

-----Can I go now?

----- Yes, you can. / No, you can’t.

3) 表示客观可能性（客观原因形成的能力）。

They’ve changed the timetable, so we can go by bus instead.

This hall can hold 500 people at least.

4) 表示推测（惊讶、怀疑、不相信的态度），用于疑问句、否定句和感叹句中。

Can this be true?

This can’t be done by him.

How can this be true?

二．should,

1) should,表示 应该 劝告、建议和命令。

1. I should help her because she is in trouble.

1. You should go to class right away.

2. Should I open the window?

3) 表示推测

Should（客观推测） , must (主观推测)。

1. He must be home by now. (断定他已到家)

2. He should be home by now.(不太肯定)

(一) 用适当的情态动词填空。

1. Must I stand up? No, you ________.

2. ________ I speak something? Yes, you ________.

3. ________ I leave the park now? No, you _________ stay here.

4. My grandmother is ill. I _________ stay at home and look after her.

5. ________ you like some juice?

6. They ________ take more exercise.

7. ________ you tell me the way to the museum?

8. The watch ________ tell us the right time.

9. ________ you like to go boating with us?

10. ________ we play chess next weekend?

(二) 按要求改写句子。