if条件状语从句及其时态的用法.ppt

if条件状语从句及其时态的用法,英国前首相撒切尔夫人（Margaret Thatcher）曾用if条件句对男人和女人进行评价： In politics, if you want someone to make a speech, ask a man; if you want something done, ask a woman.,一、概念,连词if的意思是“如果”，它引导的句子表示某事发生所需要的条件，即“在条件下某事才能发生”，在句子中充当状语，因此我们称之为条件状语从句。在复合句中连词if引导的句子为从句，被修饰的句子为主句。从句可以放在主句后，也可以放在主句前，从句放在主句前时，应用逗号将它与主句隔开。例如： Well go to the Great Wall if it doesnt rain tomorrow. = If it doesnt rain tomorrow, well go to the Great Wall.,二、用法,1. 条件状语从句通常由连词if引导，意为“如果，假如”，主句不能用be going to 表示将来，而应该用shall或will。例如： If Im free tomorrow, Ill go with you. 2. if引导的条件状语从句，主句用一般将来时，从句则用一般现在时，即“主将从现”。例如： If it is sunny tomorrow, Ill climb the hill.,3. 正确区分if引导的条件状语从句和if引导的宾语从句：在条件状语从句中，if表示“如果”；而在宾语从句中，if表示“是否”。可以用下面的方法区分： 1) 从句前置法：if引导的条件状语从句，可以放在主句之前并用逗号隔开，也可放在主句之后；而if引导的宾语从句只能放在主句之后。因此如果把if放在主句之前，句子通顺，意义不变，则是条件从句，否则是宾语从句。例如： He will help you if you ask him. = If you ask him, he will help you.,2) whether替换法：if引导宾语从句时，其意为“是否”，通常可用whether替换，意义不变，而if引导条件状语从句时不能用whether替换。因此，可用whether替换的是宾语从句，不能替换的是条件从句。例如： I want to know if you will go tomorrow. = I want to know whether you will go tomorrow. 注意：区分if的用法有着极为重要的意义，因为在条件状语从句中，主句用将来时，从句用一般现在时；而在宾语从句中，当主句是一般现在时，从句可用所需的任何时态，主句是一般过去时，从句用过去的某种时态。,巩固练习,一、单项选择 1. If you _ to the party, youll 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? Well go to the library tomorrow if it _. A. isnt rain B. rain C. wont rain D. doesnt rain 4. Do you know when he will come back tomorrow? Sorry, I dont know. When he _ back, Ill tell you. A. comes B. will come C. come D. may come,5. Ill 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. Ill 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 wont go if it _ tomorrow. A. rain B. is raining C. rains D. will rain,二、用所给词的适当形式填空 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.如果他迟到了，会发生什么事情？ What _ _ if he _ late? 2. 如果努力学习，你就会取得好成绩。 If you_ _, you _ _ good _. 3. 他如果看电视太久了，他的父母会不高兴。 If he _ TV too much, his parents _ _ unhappy. 4. 如果我们为他举办生日聚会，大家都会来的。 Everyone _ _ if we _a birthday party _ him.,5. 如果明天不下雨，我会和你一起去公园的。 If it _ _ tomorrow, I _ go to the park _ you. 6. 如果她睡过头了，就会误了开会的。 She _ _ _ _ the meeting if she _ _. 7. 如果他有空，他会帮助你的。 If he _ _, he _ _ you. 8. 如果Tom考试不及格，他就没有机会上高中了。 Tom _ miss the chance to go to the high school if he _ the exams. 9. 你如果抄同学的作业就不能学好各门功课。 You _ _ good at all the subjects if you _ the other students homework.,