条件状语从句

条件状语从句预习：1.什么是条件状语从句？2.条件状语从句如何与主句时态搭配？条件状语从句经典例句：1.Ifyoustickapinintoaballoon,itbursts.2.Unlessyoukeepicecreaminafridge,itmelts.一、什么是条件状语从句？在某种条件下，可能发生某事。而由if/unless引导的表示条件的句子，就叫条件状语从句。eg:Ifyougetupearly,youwillcatchthebus.Ifyouputwoodintowater,itfloats.二、时态1．当主句和从句所表示的是原理、客观真理、规则时，主句是一般现在时（包括祈使句和含有情态动词can/may/must等），从句也要用一般现在时。例如：1)Ifyouputapieceofpaperintowater,itgetswet．如果你把一张纸放进水中，它会变湿。(原理)2)Becarefulifyoucrosstheroad.(祈使句)3)Youmustseethedoctorifyouareill.(含有情态动词）2.在if条件状语从句中，如果从句谈论的是一个可能发生的事实及其产生的相关结果，主句用一般将来时，从句用一般现在时。eg:1)Ifitrainstomorrow,wewillnotgotothezoo.2)Ifyougotobedearlier,youwon'tfeeltiredinthemorning.3.如果从句用现在进行时或现在完成时，主句需用一般将来时。1）IfyouarelookingforPeteryou’llfindhimupstairs.如果你是在找彼得，上楼就会找到他。2）IfyouhavefinisheddinnerI’llaskthewaiterforthebill.如果你吃完了，我就叫服务生来算账。三、条件状语在句中的位置大多数情况下，if/unless从句既可以放在主句之前也可以放在主句之后。当从句置于主句之前时，常用逗号与主句隔开。Itfloatsifyouputwoodintowater.=Ifyouputwoodintowater,itfloats.四、转换1、当主语是you时,if引导的条件状语从句可与“祈使句+and／or+简单句”进行句型转换。and表示句意顺承；or表示转折，意为“否则”。例如：Takecare,oryou'llfalloffthetree.小心，否则你会从树上掉下来。=Ifyoudon'ttakecare,you'llfalloffthetree.2.unless也可引导条件状语从句，相当于if...not，意思是“如果不、除非”。例如：YouwillfailinMathunlessyouworkharder.=YouwillfailinMathifyoudon'tworkharder.你要是不再加把劲儿，数学考试就不及格了。五、拓展1.if从句还可以表示不可实现的条件或根本不可能存在的条件，也就是一种虚拟的条件或假设，从句多用一般过去时或过去完成时，主句则用虚拟语气。1)IfIwereyou,Iwouldinvitehimtotheparty.2)IwouldhavearrivedmuchearlierifIhadnotbeencaughtinthetraffic.2.if表示“是否”时引导宾语从句，意思同whether.Idont'knowifhecancome.Ifhecomes,I'lltellyouatonce.一、用括号内单词的适当形式填空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.Ifyou______(need)theinstructionsinEnglish,gotoourwebsite.7.Ifthegreenlight______(notbe)on,wemustwaitforoneminute.8.Idon'tknowifhe_____(come)tomorrow.9.Ifyoudon'tputfishbacktowater,it____(die).10.Don'tgoouttomorrowifit______(rain).二、同义句转换1.Playsomesports,andyou'llbehealthy._________playsomesports,you'llbehealthy.2.Ifyoustudyhard,youwillcatchupwithyourclassmates._____youstudyhard,youwon'tcatchupwithyourclassmates.3.Fishwilldiewithoutwater.Fishwilldie_____thereisnowater.4.Don'tstayuplater,orwon'tbesleepytomorrow.____you____stayuplate,youwon'tbesleepytomorrow.5.IwillcometoseeyouunlessIamtoobusy.____Iam____toobusy,Iwillcometoseeyou.三根据汉语提示完成句子1.如果我有时间的话，我就会去帮你。IfI______,I______youwithit.2.如果明天不下雨，我们就去徒步旅行。Ifit______tomorrow,we'llgohiking.3.我们没有人能赶上汤姆，除非他不跑。Noneofuscan_________Tom___hedoes'trun.4.他不会迟到的，除非他生病。He______late___he___ill.5.如果你看见汤姆，叫他来我办公室。___Tomtocometomyoffice___you___him.Goodmorning,ladiesandgentlemen!MayIhaveyourattention,please?I'mavolunteerandI'mgladtotellyousomethingaboutprotectingthebeachesinShenzhen.Asweknow,beachesaregreatplacesforustotravelandrelax.Inordertoprotectthebeaches,ourgovernmenthasmadesomestrictrules.However,somecitizensdon'tunderstandit.Inmyopinion,thesestrictrulescanhelpuscreateabetterbeachenvironment.Thebeacheswillbecleanerandmorebeautifulifeachtouristcanrealizetheimoportanceofprotectingthem.SoIhopeallofuswilltrytofollowthese:Neverthrowrubbisheverywhere.Don'tsteponthegrassorpickflowersnearthebeach.Inaword,beachesareanimportantpartofourlivingenvironment;weallneedtotryourbesttoprotectthem.（小结）Thankyouforyourlistening.Haveaniceweekend!