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八年級語法:if條件狀語從句及其時態(tài)的用法

 家有學子 2020-09-11
概念引入

英國前首相撒切爾夫人(Margaret Thatcher)曾用if條件句對男人和女人進行評價:

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”,在句子中充當狀語,因此我們稱之為條件狀語從句。在復合句中連詞if引導的句子為從句,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,應用逗號將它與主句隔開。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,意為“如果,假如”,主句不能用be going to 表示將來,而應該用shall或will。例如:

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

2. if引導的條件狀語從句,主句用一般將來時,從句則用一般現(xiàn)在時,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引導的條件狀語從句和if引導的賓語從句。

    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”??梢杂孟旅娴姆椒▍^(qū)分:

    1) 從句前置法:if引導的條件狀語從句,可以放在主句之前并用逗號隔開,也可放在主句之后;而if引導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,他會幫助你。

2) whether替換法:if引導賓語從句時,其意為“是否”,通??捎脀hether替換,意義不變,而if引導條件狀語從句時不能用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,因為在條件狀語從句中,主句用將來時,從句用一般現(xiàn)在時;而在賓語從句中,當主句是一般現(xiàn)在時,從句可用所需的任何時態(tài),主句是一般過去時,從句用過去的某種時態(tài)。

鞏固練習

一、單項選擇

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,會發(fā)生什么事情?

    What _______ ________ if he _______ late?

2. 如果努力學習,你就會取得好成績。

    If you_______ _______, you _______ _______ good _______.

3. 他如果看電視太久了,他的父母會不高興。

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

4. 如果我們?yōu)樗e辦生日聚會,大家都會來的。

    Everyone _______ _______ if we _______a birthday party _______ him.

5. 如果明天不下雨,我會和你一起去公園的。

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

6. 如果她睡過頭了,就會誤了開會的。

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

7. 如果他有空,他會幫助你的。

    If he _______ _______, he _______ _______ you.

8. 如果Tom考試不及格,他就沒有機會上高中了。

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

9. 你如果抄同學的作業(yè)就不能學好各門功課。

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

參考答案

一、單項選擇。

1. C。本題是if引導的條件狀語從句,主句用一般將來時,從句用一般現(xiàn)在時,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引導的條件狀語從句,主句用一般將來時,從句用一般現(xiàn)在時,從句的主語為單三,動詞后加-s,所以答案為D。

3. D。條件狀語從句,主句用一般將來時,從句用一般現(xiàn)在時,rain在此是實義動詞“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引導的時間狀語從句。

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作,但只有選項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,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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