iii. must, have to, have got to

1. must的基本用法：

1）表示义务、命令或必要，“必须，应当，务必”。

I must go now, or I'll be late.

我必须走了，否则我要迟到了。

2）表示不可避免性或肯定性，“必定会，很可能”。

You mus t be hungry after your long walk.

你长途跋涉之后肯定会饿的。

3）否定式mustn't表示禁止；must的疑问句通常用needn't回答，而不用mustn't。

You mustn't keep us all waiting here.

你一定不要让我们都在这里等着。

—Must I open the box myself?

—No, you needn't .

——我必须亲手打开箱子吗？

——不，你不必要。

2. must在应用中须要注意的问题：

1）must意为“一定”，表示有把握的肯定推测，只用于肯定推测时，其否定推测是can't意为“一定不”，而不是 mustn't。

Her eyes are red. She must have been crying.

她的眼睛红红的，肯定一直在哭。

You mustn't play with fire, for you might get burnt.

你一定不要玩火，因为会烧着你的。

2）must have done表示对过去情况有把握的肯定推测；只用于表示肯定推测，其否定式为：can't have done sth.。

He can't have been to your home. He doesn't know your address.

他肯定没有去过你家里，他不知道你的地址。

3）must表示推测时的反意疑问句：

a. 对现在推测，若陈述部分是must be，多用isn't/aren't反问；若陈述部分是“must+其他动词”，多用doesn't/don't反问。

She must b e waiting for us, isn't she?

她肯定是在等我们，是吗？

He must live nearby, doesn't he?

他肯定就住在附近，是吗？

b. 对过去推测，若带有过去时间状语，陈述部分是must have been, 用wasn't/weren't反问；陈述部分是“must have+其他动词的过去分词”，用didn't反问。

He must have been to Nanjing three years ago , wasn't he?

他三年前肯定去过南京，是吗？

He must have got the letter yesterday , didn't he?

他昨天肯定收到了那封信，是吗？

c. 对过去推测，若没有过去时间状语，或者是现在完成时的时间状语，不管陈述部分是must have been还是“must have +其他动词的过去分词”，都用hasn't/haven't反问。

He must have got the letter, hasn't he?

他肯定收到了那封信，是吗？

She must have been to America before, hasn't she?

她以前肯定去过美国，是吗？

4）表示“必须”时，must强调主观，have to (Am. E) = have got to (Bri. E)强调客观，意为“不得不”。

They had to put off the sports meet because of the bad weather.

由于糟糕的天气他们不得不推迟运动会。

You don't have to pay for the books, for they are free of charge.

你不必为这些书本付款，因为它们是免费的。

专项练习

1. Where is my pen? I _______ it.

A. might lose

B. would have lost

C. should have lost

D. must have lost

2. The house is dark and quiet, so the Browns _______ have gone to bed.

A. must

B. should

C. ought

D. would

3. —Must we do it now?

—No, you _______.

A. needn't

B. mustn't

C. won't

D. shouldn't

4. —Must we take a bus?

—No, you _______. You can walk from here.

A. must not

B. don't must

C. don't have to

D. had better not to

5. —May I stop work a little earlier tonight?

—No, you _______.

A. needn't

B. mustn't

C. can't

D. don't

答案速查　1-5　DAACB