原因狀語從句because,since,as,for,這幾個(gè)詞都是表示“原因”的連詞，語氣由強(qiáng)至弱依次為：because＞since＞as＞for

其中because,since,as均為從屬連詞，引導(dǎo)原因狀語從句；而for是并列連詞，引導(dǎo)并列句。

1.because表示直接原因，其語氣最強(qiáng)。常用來回答why的提問Istayedathomebecauseitrained.—Whyissheabsent?

—Becausesheissick.

在強(qiáng)調(diào)句型中，只能用becauseItwasbecauseImissedtheearlybusthatIwaslateforschool.要點(diǎn)：不要把連接詞because與介詞短語becauseof(+名詞或-ing形式)相混淆；Helayinbedbecausehehadcaughtabadcold.

Helayinbedbecauseofabadcold.since表示顯然的或已為人所知的理由，

常譯為“因?yàn)椤?、“既然”，通常置于句首，表示一種含有勉強(qiáng)語氣的原因。Sinceheasksyou,you'lltellhimwhy.

Sinceeveryoneishere,let'sstart.as含義與since相同，但語氣更弱，沒有since正式Wealllikeherassheiskind.

AsIhadacold,Iwasabsentfromschool.

for表明附加或推斷的理由,它所引導(dǎo)的分句只能放在句子后部,并且前后兩個(gè)分句間的邏輯關(guān)系不一定是因果關(guān)系,其間用逗號(hào)隔開.Thedaysareshort,foritisnowDecember.Itmusthaverained,forthegroundiswet.nowthat既然.常放句首.Nowthatyouhaveleftuniversity,youwillhavetofindajob.Nowthateverybodyishere,let'sbeginthediscussion.1.Don’tbeafraidofaskingforhelp____itisneeded.A.unlessB.sinceC.althoughD.when2.Marywasmakingadress___shecutherfinger.A.whenB.whileC.asD.after3.Itwas_____backhomeafterexperiment.A.notuntilmidnightdidhegoB.untilmidnightthathedidnotgoC.notuntilmidnightthathewentD.untilmidnightwhenhedidnotgo4.UnlikewatchingTV,readingisahighlyactiveprogress(過程),___itrequiresattentionaswellasmemoryandimagination.A.untilB.butC.unlessD.for5.ShethoughtIwastalkingaboutherdaughter,___,infact,Iwastalkingaboutmydaughter.A.whomB.whereC.whichD.while6.____quiterecently,mostmothersinBritaindidnottakepaidworkoutsidethehome.BeforeB.UntilC.FromD.Since7.____youareleavingtomorrow,wecaneatdinnertogethertonight.ForB.SinceC.BeforeD.While

8.MrBrownreturnedhomejust___hisfamilywerehavingsupper.AthenBasCwhenDwhile9._______hetookpartinthecompetition,hewonasecondprize.AThefirsttimeBForthefirsttimeCAtthefirsttimebecause1.語氣強(qiáng)，可放在主句前或后，表示直接因果關(guān)系，回答why提出的疑問句，用在強(qiáng)調(diào)句式結(jié)構(gòu)中。漢語中的：“因?yàn)?----所以------”在英語中的表達(dá)只能使用because或so中的一個(gè)，不能同時(shí)使用這兩個(gè)單詞。1.那個(gè)男孩因病缺席。

Theboywasabsentbecausehewasill.Itwasbecausehewasillthattheboywasabsent.

2.-----Whycan'tyougotherenow?------_____I’mtoobusy.3.(Trueorfalse)BecuseIhadnothingbettertodo,soIdecidedtogotoWufengMountainwiththem.

because要點(diǎn)：不要把連接詞because與介詞短語becauseof(+名詞或-ing形式)相混淆；Helayinbedbecausehehadcaughtabadcold.Helayinbedbecauseofabadcold.1.Tomwaslateforschool.That’s_____hegotuptoolate.2.Tomgotuptoolate.That’s_____hewaslateforschool.thisis/thatis/itisbecause后面接原因。thisis/thatis/itiswhy后面接結(jié)果-----WhoknowswhereTerryis?-----Thereason_____Terryisabsentis______hisfatherhadanaccident.

Awhy;becauseBwhy;thatCthat;becauseDthat;/as表示十分明顯的原因，一般說明因果關(guān)系，著重點(diǎn)在主句，語氣比because弱，常譯為“由于”。as引導(dǎo)的從句可放在句首或句末。1.由于正在下雪，我們不去公園了。Asitissnowing,weshallnotgotothepark.2.由于我沒有讀過這本書，所以我無法告訴你有關(guān)它的事情。

AsIhavenotreadthebook,Icannottellyouanythingaboutit.1.(2012重慶)------Coach,canIcontinuewiththetraining?-------Sorry,youcan’t______youhaven’trecoveredfromthekneeinjury.

AuntilBbeforeCasDunless2.Do______youaretoldto,oryou’llbefired.AasBwhileCbeforeDsince3.________thedaygoeson,theweatherisgettingcolderandcolder.AWithBSinceCWhileDAs變成with的復(fù)合結(jié)構(gòu)

Withthedaygoingon

3.since一般表示對(duì)方已知的，無需加以說明的既成事實(shí)的理由，全句中心在主句，語氣比because和as弱，常譯為“既然”。now(that)與since意思接近，表示“既然，鑒于”。表示一種含有勉強(qiáng)語氣的原因。since和nowthat引導(dǎo)的從句常放在句首。1.既然你要去，我也要去。Sinceyouaregoing,Iwillgo.2.Sinceyouaregrownup,youshouldnotrelyonyourparents.1.(2005北京)Itisalmostfiveyears______wesaweachotherlasttime.

AbeforeBsinceCafterDwhen2.(2011四川)Asisreported,itis100years______QinghuaUniversitywasfounded.(whenbefore,after,since)

3.-----Howlongisit_____hearrivedhere?------Abouthalfanhour,Isuppose.AsinceBbeforeCwhenDafter1.(NMET1999)_______you’vegotachance,youmightaswellmakefulluseofit.

ANowthatBAfterCAlthoughDAssoonas2.____noonehasreadthebook,wecan'tdiscussit.3.____therainhasstopped,let'sgohomeatonce.(since,nowthat)A

Since

Nowthat1.既然雨已停了，讓我們立刻回家吧。

Nowthattherainhasstopped,let'sgohomeatonce.2.既然沒有人讀過這本書，我們就不能對(duì)它進(jìn)行討論。

Sincenoonehasreadthebook,wecan'tdiscussit.for意思是“因?yàn)椤?，但它不是從屬連詞，而是并列連詞，是用來說明，補(bǔ)充解釋或表示一種推理，它所引導(dǎo)的分句只能放在句子后部,并且前后兩個(gè)分句間的邏輯關(guān)系不一定是因果關(guān)系,其間用逗號(hào)隔開.1.我們得早點(diǎn)出發(fā)，因?yàn)槲覀冇泻荛L(zhǎng)一段路要走。Wemuststartearly,forwehavealongwaytogo.Itmusthaverainedlastnight,forthegroundiswet.1.(2008山東)Hefounditincreasinglydifficulttoread,_______hiseyesightwasbeginningtofail.

AthoughBforCbutDso2.（2006湖南）Amancannotsmilelikeachild,_______achildsmileswithhiseyes,whileamansmileswithhislipsalone.

AsoBbutCandDfor1._____(Because,For,As,Since)hermotherwasill,thegirlhadtostayathometolookafterher.2.Iamsoglad,______(for,as,since,nowthat)thebirdissinginganditissunny.3._____(Since,Before,As,When)timewenton,Einstein'stheoryprovedcorrect.1.(2010遼寧)The