一、must的用法

1）表示主观的义务和必要, 主要用于肯定句和疑问句, 意思为 "必须......，得......，要......"；由must引起的疑问句，肯定回答要用must或have to, 否定回答要用needn't或don't have to, 意思是"不必"；must的否定形式mustn't表示禁止，意思是"不能，不许"。如：

We must find a good method to learn computer well.

我们必须找一个学好电脑的方法。

-Must I finish the task right now?

我现在必须完成这个工作吗？

-Yes, you must. / Yes, you have to. 是的。

(-No, you needn't. / No, you don't have to. 不，不必。)

You mustn't come here without permission. 未经允许，你不能来这儿。

2）表示肯定的猜测，常用于肯定句中，意思为 "一定是, 必然......"。

注意must表示推断或猜测的几种情况:

Your sister must be a doctor in this hospital. （现在的猜测）

你姐姐一定是这家医院的医生。

He must be reading newspapers in the reading room now.

（正在进行的猜测）

他此刻一定正在阅览室读报。

It must have rained last night, for the ground is wet. （过去的猜测）

昨晚一定下雨了，因为地面上是湿的。

二、have to / have got to 的用法

1）must表示一种主观的需要，而have to 表示一种客观的需要，意思是"不得不"。 如：

I have to attend an important meeting this afternoon.

今天下午我不得不参加一个重要的会议。

Mother is out, so I have to look after the shop.

妈妈不在家，因此我不得不照看商店。

2）have to 的否定形式是don't have to, 相当于needn't。如：

They don't have to buy a computer at present.

他们目前没有必要买电脑。

3）have to 与have got to 常可以互换。

三、巩固练习：

从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。

1. Mike, you ______ play with fire. You______ burn yourself.

A. won't; can't B. mustn't; may

C. don't have to; must D. have got to; shouldn't

2. You ______ see the doctor, Joe. You don't look very well.

A. must B. shall

C. may D. can

3. -Must I clean the window now?

-No, you ______.

A. mustn't B. needn't

C. can't D. may not

4. Jack's ill, so they ______ change their plans.

A. must B. should

C. have got to D. ought to

5. Harry has been reading all day -he ______ be tired.

A. should B. has got to

C. has to D. must


Key 1: 1-5 BABCD
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