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Unit7Theunknownworld第3课时——语法课后拓展课时精讲栏目导航课时过关单元语法讲解：原因状语从句（Adverbialclausesofreason）1．定义：在句中用来说明主句原因的句子叫原因状语从句。2．常用引导词:because（因为），as（由于），since（既然），nowthat（既然）3．时态：原因状语从句一般都是根据实际情况选用适当的时态。通常是主过从过，主现从现。4．because,since和as的区别：（1）because引导的原因状语从句一般放于主句的后面，because从句位于句首时要用逗号分开，放在句中时，可不用逗号分开。because表示直接原因，语气最强，最适合回答why引导的疑问句。becauseof也表示原因，但它后面不接从句，只能接名词，代词或名词性短语。注意：because和so不可同时出现在一个句子里。Wewentbybusbecauseitwascheaper.=Itwascheapersowewentbybus.我们乘公交汽车去，因为这样便宜一些。Hecan’tgotoschooltodaybecauseofhisillness.他今天病了，不能去上学。—Whynotgoouttoplayfootballwithus?—为什么不和我们一起去踢足球呢？—Becausemyparentsarenotathome.Ihavetolookaftermyyoungersister.—因为我父母不在家，我得照顾我的妹妹。（2）since引导的原因状语从句一般放于主句之前表示已知的、显然的理由（通常被翻译成“既然”=nowthat），较为正式，语气比because弱。Sinceyouarefreetoday,youhadbetterhelpmewithmymathematics.既然今天你休息，你最好帮我补习数学。Sinceyoudon’ttrusthim,youshouldnotemployhim.你既然不信任他，你就不该雇用他。Nowthatyouaregrownup,youshouldnotrelyonyourparents.既然你长大了，就不该依靠你的父母了。（3）as引导原因状语从句时表示附带说明的“双方已知的原因”，含有对比说明的意味，语气比since弱，较为正式，位置较为灵活（常放于主句之前）。Asitisraining,you’dbettertakeataxi.由于正在下雨，你最好乘坐出租车。Asyouaretired,youhadbetterrest.由于你累了，最好休息一下吧。Iwenttobedearly,asIwasexhausted.我睡得早，因为我精疲力尽了。（4）for引导的是并列句表示原因但并不说明主句行为发生的直接原因，只提供一些辅助性的补充说明，for引导的并列句只能放于主句之后并且必须用逗号将其与主句隔开。Hecouldnothaveseenme,forIwasnotthere.他不可能见过我，因为我不在那里。Heseldomgoesoutnow,forheisveryold.他现在难得出门了，因为他年事已高。一、单项选择。（）1．_______Janewastheeldest,shelookedaftertheothers.A．ThoughB．IfC．As（）2．_______youknowit,Iwon’tsaiditagain.A．SinceB．AlthoughC．IfCA（）3．Hedidn’theartheknockatthedoor_______hewaslisteningtotheradio.A．sinceB．asC．because（）4．—Whydidn’tyoucome?—________mymotherwasill.Ihavetotakecareofher.A．UnlessB．BecauseC．IfCB（）5．________everybodyishere,let’sbeginthediscussion.A．NowthatB．AlthoughC．But（）6．Idoit_______Ilikeit.A．whyB．becauseC．though（）7．_______youarefreetoday,youcanhelpyourmotherwiththehousework.A．SinceB．AfterC．UntilABA（）8．_______youaregrownup,youshouldnotrelyonyourparents.A．UnlessB．ThoughC．NowthatC（）9．________youaretired,youhadbetterrest.A．AsB．WhyC．Before（）10．_______you’vegotachance,youshouldmakegooduseofit.A．UnlessB．SinceC．AlthoughAB二、用所给词将下列句子合成一个句子。1．Tobywasnotabletosolvetheproblem.Itwastoodifficult.（as）Astheproblemwastoodifficult,Tobywasnotabletosolveit.2．Jennyhadtochangeherclothes.Shegotallwetintheheavyrain.（since）SinceJennygotallwetintheheavyrain,shehadtochangeherclothes.3．Icouldn’tgettosleep.Itwasnoisyoutside.（because）Icouldn’tgettosleepbecauseitwasnoisyoutside.4．Myparentsdidn’tpickmeupyesterday.Theywerebusy.（since）Sincemyparentswerebusy,theydidn’tpickmeupyesterday.5．IlikemyChineseteacher.Heisfriendly.（becauseof）6．Maryhasalotoffriends.Sheiskind.（because）IlikemyChineseteacherbecauseofhisfriendliness.Maryhasalotoffriendsbecausesheiskind.一、完形填空。Agreenlifesometimesjustneedsagoodidealikesharingcars（共车）．It’sanewwayofthinking.Youcanuseacarbutyoudon’tneedtoownit.Nowtheideaof“carsharing”hasbecome1inmanycountries.Asweknow,mostcars2ingaragesformuchtime.Infact,wedriveourowncars3oneortwohoursadayonaverage.Whenwedon’tusethem,wehavetopayforparkingand4things.Thatcoststoomuchmoney.To5money,somepeoplecomeupwiththeideaof“carsharing”.Ifweshareacar,we’llonly6whenweuseit.Nowmanypeoplearestartingtodocarsharing.InSwitzerland,almost40,000peoplehave7it.Japanisalsotryingtomake8populararoundthecountry.Carsharingisthebeginningofanewideain9.Itisalsoverygoodforustotraveleverywhere10buyingacar.Doyoulovetoshareacarwithothers?（）1．A．popularB．interestingC．funny（）2．A．arewashedB．aredrivenC．areparked（）3．A．asfarasB．aslongasC．asmuchas（）4．A．otherB．theotherC．another（）5．A．makeB．saveC．haveACBAB（）6．A．spendB．costC．pay（）7．A．joinedB．coveredC．dropped（）8．A．timesavingB．moneysavingC．carsharing（）9．A．fashionB．transportationC．people（）10．A．withoutB．withC．byCACBA二、Morepractice语法填空。UFOManypeoplesaytheyhaveseenUFOs.Hereisonefamousstory.It（1）（call）theRoswellIncidentandithappenedintheUSin1947．iscalledPersonA:MywifeandIweresittingoutside（2）itwasawarmnight.Suddenlywesawsomethingverybright（3）（fly）throughthesky.PersonB:Ifoundsomepiecesofstrangemetalonmyfarm.Icalledthearmy.MajorMarcelcameand（4）（collect）thepieces.Hetoldmenot（5）（talk）toanyoneaboutthis.becauseflyingcollectedtotalkPersonC:Iwentandcollectedthepieces.Igave（6）（they）toanarmyexperts.Hesaidthepiecescame（7）aweatherballoon.（8）,sinceIhavenotseenthiskindofmetalbefore,Ithinkthiswas（9）lie.themfromHoweveraPersonD:MyparentsandIwereinthecountryside.（10）（sudden）wesawasilverspaceshiponthesideofthehill.Therewerethebodiesofthreealienslyingonthegrass.Thensomesoldierscameandtoldustoleave.Suddenly