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

(二)虚拟语气

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.

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 .

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 .

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 .

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 .

2、含有情态动词的句子改为否定句或疑问句不必加助动词，只需要将情态动词置于主语前，或在情态动词后加上not。

例如：Must I write a letter to cheer him up?

You needn’t wait for me.

情态动词的过去式，例如can-could，may-might。但是少数情态动词只有过去式，例如used to表示过去常常。must的过去式往往用had to代替。

情态动词后还可接不定式的进行式、完成式和被动式。

例如：He can’t be doing his homework now. 他现在不可能在做功课。

He must have attended the meeting last night. 昨晚他一定参加了会议。

(一)情态动词

1、情态动词在句中没有人称和数的变化。

虚拟语气表示说话人的意愿、假设、猜测或建议。虚拟语气不表示客观存在的事实，谓语动词用特殊的形式表示虚拟语气。

表示与现在事实相反时的谓语形式。

例如：If Tom were hungry, he would eat the bread. (In fact, Tom isn’t hungry.)

表示与过去事实相反的谓语形式。

例如：If I had left a little earlier, I would have caught the early bus. (In fact, I didn’t catch the bus.)

表示与将来事实相反的谓语形式。

例如：If they came tomorrow, we would told them about it. (In fact, they won’t come tomorrow。)

动词wish后的宾语从句中，谓语动词可用过去式、过去完成式或would、might加原形。

例如：I wish I were as strong as you.

He wished I would stay with us.

She wished I had attended the meeting yesterday.

在有些动词如：suggest、insist、order等动词后，从句谓语动词用“should + 动词原形”，should可以省略。例如：

He suggested that we (should) discuss the problem right now.

在有些句型中如：It is important (necessary、natural、strange等) + that从句中的谓语动词用should + 动词原形，should可以省略。例如：

It is necessary that the doctor (should) be sent there at once.

在It is time that, I would rather that句式中从句谓语动词用过去式。例如：

It is time we went to bed.

I would rather he came next week.

第二节 实战演练

4. must与have to比较

must侧重于个人意志和主观上的必要，have to侧重于客观上的必要。如果用于过去时态或将来时态时，则要用have to的相应时态来代替must。但must可用于间接引语中表示过去的必要或义务。

My brother was very ill，so I had to call for the doctor in the middle of the night.

我弟弟病得很厉害，我只得半夜里把医生请来。(一般过去时)

I haven't got any money with me，so I'll have to borrow some from my friend.

我身上没有钱，只好向朋友借点了。(一般将来时)

He said that they must work hard.他说他们必须努力工作。

3. have to的疑问句

句型：Do(Does, Did, Will)+主语+have to +动词原形？

Do you have to study maths now？

你现在必须学数字吗？

Yes，I do.是的，必须学。

No，I don't(have to)。不，不必学。

Did he have to ask the question？

他非要问那个问题吗？

Yes，he did.是的。

No，he didn't(have to).不。

2. have to的否定句

句型：主语+don't(doesn't, didn’t, will not)have to+动词原形

You don't have to walk so fast.

你不必走那么快。

He will not have to buy a new coat next year.

明年，他没必要买新外衣了。

1. have(has)to +动词原形

have(has)to后面要用动词原形。当主语为第三人称单数时用has to，当句子是过去时用had to。

We have to leave now.

我们不得不现在就离开。

He has to work on Sunday.

他不得不在周日工作。

I had to do my homework last Sunday.

上周日，我不得不做作业。