If 用法汇总1、主将从现（主句为一般将来时,从句为一般现在时）；eg:If it rains(从句) ,I will stay at home（主句）.=I will stay at home if it rains.2、主句含有情态动词（must、may、can etc.）从句为一般现在时；eg:If you drive too fast ,you may have an accident.=You may have an accident if you drive too fast3、主句为祈使句,从句要用一般现在时态；eg:Don't play computer games if you don't finish your homework. 4、是否=whetherAsk if he is at home. I wonder if she is ill.5、虚拟语气eg:If I were a bird ,I would fly in the sky.（事实我不可能是鸟）时态：可以表示过去，现在和将来的情况，它的基本特点是时态退后.a.同现在事实相反的假设从句用一般过去时should( would) +动词原形If they were here,they would help you.b.表示于过去事实相反的假设从句用过去完成时should(would) have+ 过去分词If she had worked harder,she would have succeeded.If my lawyer had been here last Saturday,he would have prevented me from going.c.表示对将来的假想一般过去时，were+ to do，从句：主+ should/would/could/might+v原形should+ v原形，If you succeeded,everything would be all right.If you were to succeed,everything would be all right.If you should succeed,everything would be all right.单项练习（每个必须让学生翻译）1. If I _____ where he lived, I _____ a note to him.A. know, would have sentB. had known, would have sentC. know, would sendD. knew, would have sent2.Mary is ill today. If she _____, she _____ absent from school.A. were not ill; wouldn’t beB. had been ill; wouldn’t have beenC. had been ill; should have beenD. hadn’t been ill; could be3. He acted as if he _____ everything in the world.A. knewB. knowsC. has knownD. won't know4. If you had enough money, what _____?A. will you buyB. would you buyC. would you have boughtD. will you have bought5. If Mr. Young _____ with justice, he _____ such a wrong thing.A. were treated; wouldn’t doB. had been treated; wouldn’t have doneC. were treated; wouldn’t have doneD. had been treated; wouldn’t do6. What _____ if there _____ no light during the day?A. will happen; wasB. would happen; isC. happens; wereD. would happen; were7. The spokesman acted that way as if he _____ anything about the accident but actually he did.A. doesn’t hearB. didn’t hearC. haven’t heardD. hadn’t heard8.If it _____ not for the fact that you _____ ill now, I would surely punish you.A. is; areB. were; wereC. were; areD. was; were9. Many Chinese movie stars now have given up their Chinese nationality. If I were them,I _____ that.A. shouldn’t doB. didn’t doC. hadn’t doneD. won’t do10. I want to get back by 5 o’clock if _____.A. likelyB. canC. possibleD. Probable11. It seems as if it _____ already summer now but it is only February.A. isB. wasC. wereD. had been12. If Henry had not pulled his cap low over his brow, he _____ by the police.A. might be recognizedB. might have been recognizedC. would have recognizedD. was to have been recognized13. There is a ring at the door. That _____ be the postman, I suppose.A. willB. wouldC. is going toD. was going to14. Look at the dark clouds—there _____ be a storm.A. willB. must have beenC. is going toD. would15. —Why are you taking the pictures down?—I _____ the wall.A. paintB. have just paintedC. am going to paintD. will have painted16. —Can I stay at home tomorrow?—Yes, you can if it_____.A. will snowB. is going to snowC. snowsD. snowed17. I don’t know if he _____ this afternoon. But if he _____, I will tell you.A. will come; will do;B. comes; will doC. will come; doesD. comes; does18. —I thought I asked you to fix the radio.—Oh, I’m sorry. I _____ it right away.A. am to doB. will doC. was about to doD. am going to do19. The WTO can’t live up to its name _____ it does not include a country that is home to one fifth of mankind.A. as long asB. whetherC. ifD. even though20. Ask him to ring me up if you _____ him.A. seeB. sawC. would seeD. will see21. It’s so late. I don’t think he ______ come.A. wouldB. shouldC. is going toD. shall22. If people _____ polluting the air, animals and plants will die soon.A. don’t stopB. didn’t stopC. shall not stopD. haven’t stopped23. If you _____ an interesting day out, ______ the Science Museum.A. want; visitingB. want; visitC. want to; visitD. wanting; visit24. If the pure water is heated to 100 centigrade degrees, it ______ boil.A. is going toB. willC. wouldD. is to25. Is a dictionary available, _____ so, where?A. ifB. if isC. and ifD. and if is1—5 BAABB 6—10 DDCAC11—15 CBACC 16—20 CCBCA 21—25 CABBC最后一练——1.If you _____ to the party, you’ll have a great time. A. will go B. went C. go D. going2. It will be a long time ____ Peter _____ his work.A. since, has finishedB. after, finishesC. when, will finishD. before, finishes.3. What will father _____ us from Japan? A. take B. bring C. carry D. make4. Weifang is famous ______ kites. A. for B. to C. on D. with5．I ____ her the answer if she ____me.A. can tell, will askB. will tell, will askC. would tell, askD. will tell, asks6. – What are you going to do tomorrow?--We’ll go to the library tomorrow if it ___.A. isn’t rainB. rainC. won’t rainD. doesn’t rain7.—Do you know when he will come back tomorrow?--Sorry, I don’t know. When he ____ back, I’ll tell you.A. comesB. will comeC. comeD. may come8. What will you do if you _____ to the old folk’s home visit?A. goB. wentC.goingD. will go9. If I eat ____ food, I’ll be very fat.A. too manyB. many tooC. too muchD. much too10. I’ll give the book to him if he ___ here next Sunday.A. will comeB. comesC. is comingD. came11. There ____an English film in our school tomorrow.A. is going to haveB. will haveC. is going to beD. has12. Could you tell us where ____？A. will the next Olympic Games heldB. the next Olympic Games will be heldC. would the next Olympic Games be heldD. the next Olympic Games would be held13. When my mother returned last night, I ____ a book.A. readB. am readingC. was readingD. am going to read14.What ____ you ____ when it began to rain?A. do, doB. were, doingC. are, doingD. did, do15. I’ll wake you up when he ____back.A. willB. is going to comeC. comesD. come1---5 CDBAD 6---10 DAACB 11---15 CBCBC。