概念引入

英國前首相撒切爾夫人(Margaret Thatcher)曾用if條件句對(duì)男人和女人進(jìn)行評(píng)價(jià)：

In politics, if you want someone to make a speech, ask a man; if you want something done, ask a woman. 在政治領(lǐng)域，如果你想要有人發(fā)表演說，那就找男士去;而如果你想真正把事情解決，那就找女士。

用法講解

一、概念

連詞if的意思是“如果”，它引導(dǎo)的句子表示某事發(fā)生所需要的條件，即“在……條件下某事才能發(fā)生”，在句子中充當(dāng)狀語，因此我們稱之為條件狀語從句。在復(fù)合句中連詞if引導(dǎo)的句子為從句，被修飾的句子為主句。從句可以放在主句后，也可以放在主句前，從句放在主句前時(shí)，應(yīng)用逗號(hào)將它與主句隔開。例如：

We’ll go to the Great Wall if it doesn’t rain tomorrow. = If it doesn’t rain tomorrow, we’ll go to the Great Wall. 如果明天不下雨，我們就去長城。

二、用法

1. 條件狀語從句通常由連詞if引導(dǎo)，意為“如果，假如”，主句不能用be going to 表示將來，而應(yīng)該用shall或will。例如：

If I’m free tomorrow, I’ll go with you. 如果我明天有空，我將會(huì)和你一起去。

2. if引導(dǎo)的條件狀語從句，主句用一般將來時(shí)，從句則用一般現(xiàn)在時(shí)，即“主將從現(xiàn)”。例如：

If it is sunny tomorrow, I’ll climb the hill. 如果明天天氣晴朗，我將去爬山。

3. 正確區(qū)分if引導(dǎo)的條件狀語從句和if引導(dǎo)的賓語從句。

在條件狀語從句中，if表示“如果”;而在賓語從句中，if表示“是否”。可以用下面的方法區(qū)分：

1) 從句前置法：if引導(dǎo)的條件狀語從句，可以放在主句之前并用逗號(hào)隔開，也可放在主句之后;而if引導(dǎo)的賓語從句只能放在主句之后。因此如果把if放在主句之前，句子通順，意義不變，則是條件從句，否則是賓語從句。例如：

He will help you if you ask him. = If you ask him, he will help you.

如果你問他，他會(huì)幫助你。

2) whether替換法：if引導(dǎo)賓語從句時(shí)，其意為“是否”，通常可用whether替換，意義不變，而if引導(dǎo)條件狀語從句時(shí)不能用whether替換。因此，可用whether替換的是賓語從句，不能替換的是條件從句。例如：

I want to know if you will go tomorrow. = I want to know whether you will go tomorrow.

我想知道你明天是否去。

注意：區(qū)分if的用法有著極為重要的意義，因?yàn)樵跅l件狀語從句中，主句用將來時(shí)，從句用一般現(xiàn)在時(shí);而在賓語從句中，當(dāng)主句是一般現(xiàn)在時(shí)，從句可用所需的任何時(shí)態(tài)，主句是一般過去時(shí)，從句用過去的某種時(shí)態(tài)。

鞏固練習(xí)

一、單項(xiàng)選擇

1. If you _____ to the party, you’ll have a great time.

A. will go

B. went

C. go

D. going

2. I ______ her the answer if she _____ me.

A. can tell, will ask

B. will tell, will ask

C. would tell, ask

D. will tell, asks

3. — What are you going to do tomorrow?

— We’ll go to the library tomorrow if it ______.

A. isn’t rain

B. rain

C. won’t rain

D. doesn’t rain

4. — Do you know when he will come back tomorrow?

— Sorry, I don’t know. When he ______ back, I’ll tell you.

A. comes

B. will come

C. come

D. may come

5. I’ll give the book to him if he ____________ here next Sunday.

A. will come

B. comes

C. is coming

D. came

6. There ____________ an English film in our school tomorrow.

A. is going to have

B. will have

C. is going to be

D. has

7. I’ll wake you up when he ____________back.

A. will

B. is going to come

C. comes

D. come

8. The football match will be put off if it ________.

A. will rain

B. rains

C. rained

D. is rained

9. There ________ a basketball game this afternoon.

A. is going to have

B. will be

C. is going to play

D. will play

10. I won’t go if it ________ tomorrow.

A.rain

B.is raining

C.rains

D.will rain

二、用所給詞的適當(dāng)形式填空

1. If you ________(feel) tired, you _________ (have) to have a rest.

2. Where ________ he ________ (see) the film if he _________(have) time?

3. If there ________ (be) fewer trees, there ________ (be) more pollution.

4. He ________ (dress) more casually if he ________ (not work) on weekends.

5. If Marcia ________ (live) alone, she ________ (keep) a pet parrot.

6. Lana ________ (buy) a new dress if the old one ________ (be) out of style.

7. The twins ________ (fight) if they________ (argue).

8. I ________ (have) a bake sale if I ________ (need) money for education.

9. Peter ________ (send) me a beautiful souvenir if he ________ (go) to Spain.

10. If Mr. Green ________ (say) I am hard- working, my parents ________ (feel) glad.

11. I ________ (go) to the beach if it ________ (not rain) this week.

12. ________they ________ (have) a match if the P.E. teacher________ (be) not busy?

13. He ________ (write) a letter to his grandparents if he ________ (get) his report card this week.

14. If she ________ (get) up late, she ________ (not catch) the early bus.

15. Peter ________ (major) in English if he ________ (pass) the exams in Peking University.

三、完成句子

1.如果他遲到了，會(huì)發(fā)生什么事情?

What _______ ________ if he _______ late?

2. 如果努力學(xué)習(xí)，你就會(huì)取得好成績。

If you_______ _______, you _______ _______ good _______.

3. 他如果看電視太久了，他的父母會(huì)不高興。

If he _______ TV too much, his parents _______ _______ unhappy.

4. 如果我們?yōu)樗�舉辦生日聚會(huì)，大家都會(huì)來的。

Everyone _______ _______ if we _______a birthday party _______ him.

5. 如果明天不下雨，我會(huì)和你一起去公園的。

If it _______ _______ tomorrow, I _______ go to the park _______ you.

6. 如果她睡過頭了，就會(huì)誤了開會(huì)的。

She _______ _______ _______ _______ the meeting if she _______ _______.

7. 如果他有空，他會(huì)幫助你的。

If he _______ _______, he _______ _______ you.

8. 如果Tom考試不及格，他就沒有機(jī)會(huì)上高中了。

Tom _______ miss the chance to go to the high school if he _______ the exams.

9. 你如果抄同學(xué)的作業(yè)就不能學(xué)好各門功課。

You _______ _______ good at all the subjects if you _______ the other students’ homework.

參考答案

一、單項(xiàng)選擇。

1. C。本題是if引導(dǎo)的條件狀語從句，主句用一般將來時(shí)，從句用一般現(xiàn)在時(shí)，即“主將從現(xiàn)”，所以答案為C。

2. D。根據(jù)句意“如果她問我，我就告訴她答案。”可知本句是if引導(dǎo)的條件狀語從句，主句用一般將來時(shí)，從句用一般現(xiàn)在時(shí)，從句的主語為單三，動(dòng)詞后加-s，所以答案為D。

3. D。條件狀語從句，主句用一般將來時(shí)，從句用一般現(xiàn)在時(shí)，rain在此是實(shí)義動(dòng)詞“下雨”的意思，故答案為D。

4. A。根據(jù)“主將從現(xiàn)”可知本句答案為A。此題是when引導(dǎo)的時(shí)間狀語從句。

5. B。根據(jù)“主將從現(xiàn)”可知答案為B。

6. C。be going to do，will do都可以表示將來的動(dòng)作，但只有選項(xiàng)C符合There be句型要求。

7. C。根據(jù)“主將從現(xiàn)”可知答案為C。

8. B。根據(jù)“主將從現(xiàn)”可知答案為B。

9. B。本題考查there be句型的一般將來時(shí)，there will be，故答案為B。

10. C。根據(jù)“主將從現(xiàn)”可知答案為C。

二、用所給詞的適當(dāng)形式填空

1. feel; will have

2. will; see; has

3. are; will be

4. will dress; doesn’t work

5. lives; will keep

6. will buy; is

7. will fight; argue

8. will have; need

9. will send; goes

10. says; will feel

11. will go; doesn’t rain

12. Will; have; is

13. will write; gets

14. gets; won’t catch

15. will major; passes

三、完成句子

1. will happen; is

2. study hard; will get; grades

3. watches; will be

4. will come; have; for

5. doesn’t rain; will; with

6. will be late for; sleeps late

7. has time; will help

8. will; fails 9. won’t be; copy

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