5. The reason why they 　　　　leave wasn't explained to us.　 　A. had　 　　　　　　 B. had to　 　　　 C. must　 　　　　　　　 D. might

4. -　　　 　I help you with some shoes, madam?

-Yes, I would like to try on those brown ones.　　　　　　

A. Will　 　　　　　　 B. Should　 　　 C. May　 　　　　　　　　 D. Must

3. He　　 　you more help, even though he was very busy.　　

　A. might have given　 　　　　　　　　　　　　　　　 B. might give 　C. may have given　　 　　　　　　　　　　　　　　 D. may give

2.You　　　 　to the meeting this afternoon if you have something important to do.　

　A. needn't to come　　 　　　　　　　　　　　　　　 B. don't need come 　C. don't need coming　　　　　　　　　　　　　　　　 D. needn't come

例1、There ____ be any difficulty about passing the road test since you have practised a lot in the driving school.

　　 A. mustn’t 　　　　 B. shan’t 　　　　　　　　　　 C. shouldn’t 　　　　 D. needn’t

答案：C

[解析]　 根据经验或惯例对某一情况进行推测，用should或ought to，常译成“按理应该…”或“可能会……”。shouldn’t是其否定形式。

例2、-Is John coming by train?

-He should, but he _______ not. He likes driving his car.

A. must　　　 B. can　　　　 C. need　　　　 D. may

答案为D。

[解析]　 come, go, leave, start等趋向动词的进行时表示将来时，所以答语是对这一将来动作做出的推断。may not“可能不；不一定”，根据he likes driving his car可以看出John可能乘火车来，也可能自己开车来。may not正好符合这一语境。must not“不准”；cannot“不可能”；need not“不必”。　

例3、It is hard for me to imagine what I would be doing today if I _______ in love, at the age of seven, with the Melinda Cox Library in my hometown.

A. wouldn't have fallen　　　 B. had not fallen

C. should fall　　　　　　　　 D. were to fall

答案为B。

[解析]　 根据句意和I would be doing可以判断这是虚拟语气。at the age of seven 是表示过去的时间状语，if从句中的谓语要用had not fallen，表示对过去情况的假设。由于主句中的谓语表示对现在的虚拟，条件句中的谓语表示对过去情况的虚拟，增加了试题的难题，但是，使用排除法可以容易地做出该题：should fall 和were to fall都可以用于条件句中表示对将来的虚拟；wouldn't have fallen不用于条件句中，所以都不能作为答案。译文：如果我不在七岁时就迷恋上了我们家乡的Melinda Cox图书馆，我真不能想象我今天会做什么。　

例4、You can't imagine that a well-behaved gentleman ________be so rude to a lady.

A. might　　　 B. need　　　　 C. should　　　 D. would

答案为C。

[解析]　 should用于表示感情，意向等句中的that从句，表示“竟然……，居然……”的惊讶，出乎意料。译文：你难以想象一位行为体面的绅士会对一位女士那么粗鲁。

例5、What would have happened ________, as far as up to the river bank?

A. Bob had walked farther　　　　 B. if Bob should walk farther

C. had Bob walked farther　　　　 D. if Bob walked farther

答案为C。

[解析]　 因为主句的谓语动词用了would have happened，所以从句的谓语动词要用过去完成时。在虚拟语气中，如果条件状语从句中的if省略，该句要倒装。译文：如果鲍勃走得远一点，走到岸边，会发生什么事呢?

例6、Mr. Bush is on time for everything. How ________it be that he was late for the opening ceremony?

A. can　　　　 B. should　　　 C. may　　　 D. must

答案为A。

[解析]　 can表示可能性的推测，常用于疑问句或否定句中；may表“可能性”常用于肯定句或否定句中；must常用于肯定句中表推测，“一定……”的意思。注意：can not表示“不可能”，而may not表示“或许不……可能不……”，两者语气上有区别。译文：布什先生按时做好一切事。他来参加开幕式迟到了可能会是什么样的情景呢?

例7、My sister met him at the Grand Theatre yesterday afternoon, so he _________ your lecture.

A. couldn't have attended　　　　　 B. needn't have attended

C. mustn't have attended　　　　　 D. shouldn't have attended

答案为A。

[解析]　 “情态动词+不定式完成式”有各自的含义。must have done表示对过去事情的肯定推测，多用于肯定句中；needn't have done表示过去本不必做的事情；shouldn't have done表示过去做了不该做的事情；can't (couldn't) have done表示对过去的否定性推测，意为“不可能”。所提供的情境My sister met him at the Grand 表示他不可能参加讲座。　

例8、He hesitated for a moment before kicking the ball, otherwise he_________ a goal.

A. had scored　　 B. scored　　　　 C. would score　　　 D. would have scored

答案为D。

[解析]　 根据otherwise可以判断出要用虚拟语气。表示过去发生的事要用would have scored。译文：在踢球前他犹豫了一会儿，否则他就会射中球门。

例9、Oh, I'm not feeling well in the stomach. I _______ so much fried chicken just now.

A. shouldn't eat　 B. mustn't have eaten　　 C. shouldn't have eaten　 D. mustn't eaten

答案为C。

[解析]　 just now是表示过去的时间状语。情态动词在表示过去发生的事时，必须用“情态动词+have+过去分词的形式”。所以只能在选项B或C中确定答案。mustn't have eaten是一个错误选项，因为“mustn't+动词”表示“禁止”，不表示判断或推测。译文：噢，我觉得胃不舒服。我刚才不应该吃那么多炸鸡。　

例10、I was really anxious about you .You_________ home without a word.

A. mustn't leave　　　　　　　 B. shouldn't have left

C. couldn't have left　　　　　 D. needn't leave

答案为B。

[解析]　 should' t have done表示本来不应该做而做了，含责备意味。译文：我真为你着急，你不应该不说一句话就离开了家。另外注意mustn't+动词表示“禁止”。　

第三节 巩固练习

Direction: Beneath each of the following sentences there are four choices marked A. B. C and D. Choose the best answer that completes the sentence.

1. -Isn' t that Ann's husband over there?

-No, it _______ be him . I'm sure he doesn't wear glasses.

A. can't　　　 　　 B. must not　　　 　　　 C. won't　　 　　　　　　　 D. may not

5、　 有suggest等词的相应的名词组成的同位语从句及表语从句用虚拟式。

例如：I accepted my mother’s suggestion that I should eat an apple every day .

4、　 有时句子通过but或otherwise等词来表示真实与虚拟的转换，在这种情况下，只有不真实的部分用虚拟式。

例如：I was ill yesterday；otherwise I would have played football with you .

But for the heavy rain , we would have gone to the concert .

3、　 某些条件可以用介词短语without… , but for 等来表示 。

例如：Without your help , I could not have succeeded in passing the exam .

2、　 should与would都可以用于if条件句的主句中，但should一般只用于第一人称，would用于所有人称。

例如：If you were here , I would tell you the news .

1、　 在if条件句中，如果含有were , should或had等助动词，if可以省去，句子用倒装。

例如：Were I you , I would buy this reference book.