高中語法專練：iii. must, have to, have got to

iii. must, have to, have got to

1. must的基本用法：

1）表示義務、命令或必要，“必須，應當，務必”。

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

我必須走了，否則我要遲到了。

2）表示不可避免性或肯定性，“必定會，很可能”。

You mus t be hungry after your long walk.

你長途跋涉之后肯定會餓的。

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

You mustn't keep us all waiting here.

你一定不要讓我們都在這里等著。

—Must I open the box myself?

—No, you needn't .

——我必須親手打開箱子嗎？

——不，你不必要。

2. must在應用中須要注意的問題：

1）must意為“一定”，表示有把握的肯定推測，只用于肯定推測時，其否定推測是can't意為“一定不”，而不是 mustn't。

Her eyes are red. She must have been crying.

她的眼睛紅紅的，肯定一直在哭。

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

你一定不要玩火，因為會燒著你的。

2）must have done表示對過去情況有把握的肯定推測；只用于表示肯定推測，其否定式為：can't have done sth.。

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

他肯定沒有去過你家里，他不知道你的地址。

3）must表示推測時的反意疑問句：

a. 對現(xiàn)在推測，若陳述部分是must be，多用isn't/aren't反問；若陳述部分是“must+其他動詞”，多用doesn't/don't反問。

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

她肯定是在等我們，是嗎？

He must live nearby, doesn't he?

他肯定就住在附近，是嗎？

b. 對過去推測，若帶有過去時間狀語，陳述部分是must have been, 用wasn't/weren't反問；陳述部分是“must have+其他動詞的過去分詞”，用didn't反問。

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

他三年前肯定去過南京，是嗎？

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

他昨天肯定收到了那封信，是嗎？

c. 對過去推測，若沒有過去時間狀語，或者是現(xiàn)在完成時的時間狀語，不管陳述部分是must have been還是“must have +其他動詞的過去分詞”，都用hasn't/haven't反問。

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

他肯定收到了那封信，是嗎？

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

她以前肯定去過美國，是嗎？

4）表示“必須”時，must強調(diào)主觀，have to (Am. E) = have got to (Bri. E)強調(diào)客觀，意為“不得不”。

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

由于糟糕的天氣他們不得不推遲運動會。

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

你不必為這些書本付款，因為它們是免費的。

專項練習

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