当陈述部分含有情态动词must, may, can’t, 且表示推测时，反意疑问部分不能用must, may, can’t自身，应和后面的实义动词保持一致，随时间和人称而变化，如何才能快速准确地做出判断呢根据笔者多年的教学经验，利用还原法解决这一问题较好。

所谓还原法，就是先把句子还原成一个不带must推测意味的句子。

如He must be a teacher.可还原为He is a teacher.其反意疑问句为isn’t he 也就是原句的正确答案。

同样方法You must have waited for a long time.可还原为You have waited for a long time.其反意疑问句haven’t you 即原句的答案。

注意：1、在must 表示现在情况的推测时，要注意主语对还原后句子谓语动词的影响。

如：1. He must be ill at home, isn’t he
（还原为He is ill at home.）
2. They must be ill at home, aren’t they
(还原为They are ill at home.)
2、must 表示对过去的情况推测时，要注意句意和时间状语对还原后句子时态的影响。

如含有for a long time, so far, before, since 等时间状语的句子还原后句子为完成时；而含有last night, yesterday, the other day, ten years ago 等时间状语的句子则还原为过去时。

如：
He must have seen her in the street yesterday, didn’t he
（还原为：He saw her in the street yesterday.）
He must have learned English for more than 10 years, hasn’t he
（还原为：He has learned English for more than 10 years.）
◆must/ may/ can’t + do 表示对现在情况的推测，反意疑问部分用一般现在时。

如：
①He must be Mr. Chen, isn’t he
(相当于：I think he is Mr. Chen.)他一定是陈先生，是吗
②He can’t be Mr. Chen, is he
（相当于I don’t think he is Mr. Chen.）他不可能是陈先生，是吗
③He must be very tired, isn’t he
(相当于：I believe he is very tired.)他一定很累，是吗
④Your mother may be at home, isn’t she
(相当于：Maybe your mother is at home.)可能你母亲在家呢，是吗
◆must/ m ay/ can’t + have done +过去时间状语，表示对过去情况的推测，反意疑问部分常用一般过去时。

如：
①He must have stayed at home yesterday, didn’t he
(相当于: I think he stayed at home yesterday.)他昨天一定呆在家里了，是吗
②You must have seen the film last week, didn’t you
(相当于：I think you saw the film last week.) 你上周一定看这部影片了，是吗
③It can’t have snowed last week, did it
(相当于：I don’t think it snowed last week.)上周不可能下雪了，是吗
④He may have gone home last night, didn’t he
(相当于：Maybe he went home last night.)他可能昨晚回家了，是吗
◆must/ may/ can’t + have done , 反意疑问部分常用现在完成时。

①You must have met him before, haven’t you
（相当于：I think you have met him before.）你从前一定见过他，是吗
②You may have been to Tibet, haven’t you
(相当于：Maybe you have been to Tibet.)你可能去过西藏，是吗
③He can’t have known the news, has he
(相当于：I don’t think he has known the news.)他不可能知道那个消息了，是吗④You must have waited for a long time, haven’t you
(相当于：I think you have waited for a long time.）你一定等了很长时间了，是吗若是被动，应按被动结构来处理。

如：
1) The room must have been cleaned yesterday, wasn't it
2) The room must have been cleaned, hasn't it
当must表示“必须、禁止“时，反意疑问部分要用must (mustn’t) 。

You mustn’t stop your car here, must you 你不能把车停在这地方，知道吗
*****当must表示“有必要”时，反意疑问句部分要用needn’t。

They must finish the work today, needn’t they 他们今天必须要完成这项工作，是吗专项练习：
1. She must have a big family, _________
2. You must be interested in the movie, _________
3. It must have rained last night, _________
4. You must have had a good time at the party, _________
5. His wife must have misunderstand him at that time, ________
6. He must have read the novel before, _________
7. They must have lived there since then, _________
8. The boy must be playing computer games in his room now, _________
9. She must have read the novel last week, _________
10. You must have told her about it, _________
11. You must have seen the play last week, _________
12. Dennis must be very tired, _________
13. Your mother must go to work by bus, _________
14. The little boy must have been ill, ________
15. He must be waiting outside, _________
16. There must be some students in the room, ________
Answers:
1. doesn’t she
2. aren’t you
3. didn’t it
4. didn’t you
5. didn’t she’t he’t they’t he
9. didn’t she10. haven’t you11. didn’t you12. isn’t he 13. doesn’t she14. hasn’t he15. isn't he 16. aren't there。