if条件状语从句及其时态的用法

if条件状语从句及其时态的用法英国前首相撒切尔夫人（MargaretThatcher）曾用if条件句对男人和女人进行评价：Inpolitics,ifyouwantsomeonetomakeaspeech,askaman;ifyouwantsomethingdone,askawoman.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：We’llgototheGreatWallifitdoesn’traintomorrow.=Ifitdoesn’traintomorrow,we’llgototheGreatWall.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begoingto表示将来，而应该用shall或will。例如：IfI’mfreetomorrow,I’llgowithyou.•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：Ifitissunnytomorrow,I’llclimbthehill.•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：Hewillhelpyouifyouaskhim.=Ifyouaskhim,hewillhelpyou.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：Iwanttoknowifyouwillgotomorrow.=Iwanttoknowwhetheryouwillgotomorrow.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.Ifyou____________totheparty,you’llhaveagreattime.A.willgoB.wentC.goD.going2.I____________hertheanswerifshe____________me.A.cantell,willaskB.willtell,willaskC.wouldtell,askD.willtell,asks3.—Whatareyougoingtodotomorrow?—We’llgotothelibrarytomorrowifit____________.A.isn’trainB.rainC.won’trainD.doesn’train4.—Doyouknowwhenhewillcomebacktomorrow?—Sorry,Idon’tknow.Whenhe____________back,I’lltellyou.A.comesB.willcomeC.comeD.maycome5.I’llgivethebooktohimifhe____________herenextSunday.A.willcomeB.comesC.iscomingD.came6.There____________anEnglishfilminourschooltomorrow.A.isgoingtohaveB.willhaveC.isgoingtobeD.has7.I’llwakeyouupwhenhe____________back.A.willB.isgoingtocomeC.comesD.come8.Thefootballmatchwillbeputoffifit____________.A.willrainB.rainsC.rainedD.israined9.There____________abasketballgamethisafternoon.A.isgoingtohaveB.willbeC.isgoingtoplayD.willplay10.Iwon’tgoifit____________tomorrow.A.rainB.israiningC.rainsD.willrain二、用所给词的适当形式填空1.Ifyou______(feel)tired,you______(have)tohavearest.2.Where______he______(see)thefilmifhe______(have)time?3.Ifthere______(be)fewertrees,there______(be)morepollution.4.He______(dress)morecasuallyifhe______(notwork)onweekends.5.IfMarcia______(live)alone,she______(keep)apetparrot.6.Lana______(buy)anewdressiftheoldone______(be)outofstyle.7.Thetwins______(fight)ifthey______(argue).8.I________(have)abakesaleifI________(need)moneyforeducation.9.Peter________(send)meabeautifulsouvenirifhe________(go)toSpain.10.IfMr.Green________(say)Iamhard-working,myparents________(feel)glad.11.I________(go)tothebeachifit________(notrain)thisweek.12.________they________(have)amatchiftheP.E.teacher________(be)notbusy?13.He________(write)alettertohisgrandparentsifhe________(get)hisreportcardthisweek.14.Ifshe________(get)uplate,she________(notcatch)theearlybus.15.Peter________(major)inEnglishifhe________(pass)theexamsinPekingUniversity.三、完成句子1.如果他迟到了，会发生什么事情？What_______________ifhe_______late?2.如果努力学习，你就会取得好成绩。Ifyou______________,you______________good_______.3.他如果看电视太久了，他的父母会不高兴。Ifhe_______TVtoomuch,hisparents______________unhappy.4.如果我们为他举办生日聚会，大家都会来的。Everyone______________ifwe_______abirthdayparty_______him.5.如果明天不下雨，我会和你一起去公园的。Ifit______________tomorrow,I_______gotothepark_______you.6.如果她睡过头了，就会误了开会的。She____________________________themeetingifshe______________.7.如果他有空，他会帮助你的。Ifhe______________,he______________you.8.如果Tom考试不及格，他就没有机会上高中了。Tom_______missthechancetogotothehighschoolifhe_______theexams.9.你如果抄同学的作业就不能学好各门功课。You______________goodatallthesubjectsifyou_______theotherstudents’homework.