before和until的用法及区别

..1.Myfriendswalkedmetothebusstopandwaitedwithme_______thebusarrived.（before；until）此题不能选before，因为时态不对。如果把walked和waited改成过去完成式hadwalked和hadwaited就可以选before。before的使用一般有强烈的时态要求而until一般没有时态要求untilIwaited_______hecameback.我一直等到他回来。Ididn'tleave______hecameback.直到他回来我才走Icanonlygiveyouananswer______Ithinkitover.untiluntilbeforeuntilbefore区别实际上，只要我们把握住两者使用时本身的含义及主句动词是终止性的，还是延续性的，肯定式，还是否定式两大点，就能容易地解决这类问题。现详细阐明如下：一、在下列情况下，两者可互换用，但含义略有不同。before表示“在……之前”的意思，强调时间先后关系；而until表示“直到……才”的意思，主句是肯定句则表示主句动作的终止时间；主句是否定句则强调主句动作的起始时间。1.主句为否定式终止性谓语动词。常见的动词是open,start,leave,arrive,finish,stop等。例如：(1)Thenoiseofthestreetdidn'tstopuntil/beforeitwasmidnight.(2)Thechildrenwon'tcomebackuntil/beforeitisdark.(3)Ididn'tleavethelovelyboyuntil/beforehismothercamehome.2.主句为肯定式、延续性谓语词，这类动词用stand,stay,talk,be,wait等。例如：(1)Helivedwithhisparentsuntil/beforehegraduatedfromschool.(2)Iwillwaituntil/beforehecomestomyhelp.(3)Ishallstayhereuntil/beforeyoucomeback.二、在下列情况下，用before不用until。1.主句这肯定式、终止性谓语动词，只用before。例：(1)HefellasleepbeforeIcouldtakeoffhisclothes.(2)Wearrivedtherebeforeitstartedtorain.(3)TheholidaycametotheendbeforeIknewit.(4)Healmostknockedmedownbeforehesawme.2.主句谓语动词强调动词的迟缓性，只用before，常伴有时间段状语或时间段暗示。例：(1)Itwasquitesometimebeforehefoundtheelephantatall.(2)Wehadwalkedalongwaybeforewefoundsomewater.(3)Wehadsailedfortwodaysbeforewesawtheland.(4)Thefirelastedaboutfourhoursbeforethefirefighterscouldcontrolit.(5)Itwasmidnightbeforemybrothercamehome.(6)Itwasthreemonthsbeforetheymetagain.3.如果强调从句谓语动作未发生，就发生主句谓语动作，只用before。常译为“未及”，“不”或“不等……就”。例：(1)Wecanleaveearlyinthemorningbeforeitgetstoohot.(2)ImustwriteitdownbeforeIforgetit.(3)Wedowanttobuysomethingnowbeforepricesgoup.4.表“与其说……倒不如”，“与其……毋宁……”只用before。例：(1)IwouldgiveupmyjobbeforeI'dagreetobedismissed.(2)Hewilldieofhungerbeforehewillsteal.5.在某些特定句型中用before。例如：(1)Itwasnotlongbeforethewholecountryroseup.(2)Itwillprobablynotbelongbeforetheyunderstandeachother.三、下列情况一般区别用until。1.主句是持续性谓语动词时，肯定、否定都可以，但意义完全不同。肯定表动作终止，而否定表动作开始。例如：(1)Wediscussedtheproblemuntil/beforehecameback.我们一直讨论到他回来。(2)Wedidn'tdiscusstheproblemuntilhecameback.我们一直等到他回来后才讨论问题。2.not…until句型尽管在某些情况下可与before互换用，但在强调句中一般仍用until。例如：(1)ItwasnotuntilhetoldmethatIknewit.(2)Itwasnotuntilhefinishedhishomeworkthathewenthome.Theyweretakingapeacefulwalkinthewoods_______threemensprangoutfrombehindabushandattackedthem.A.untilB.whenC.beforeD.afterB