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1.whether和if均可用来引导主语从句，但if引导的从句不能位于句首。如：Whethertheywinorloseisallthesametome.他们是赢是输於我都一样.（此时whether不能换作if）It'sdoubtfulwhetherthere'llbeanyseatsleft.说不上还有没有空座位了.(此句whether能换作if)2.whether和if均可用来引导宾语从句。如：①Idon'tknowwhether/ifIwillbeabletocome.我不知道我是否能来.②Sheaskedmewhether/ifIwasinterestedinworkingforher.她问我是否有兴趣为她工作。③We'llbetoldtomorrowwhetherweshouldtaketheexamornot.我们明天才知道是不是应该参加考试.④Iaskedhimwhetherhehaddonealltheworkhimselforwhetherhehadhadanyassistance.我问他这些工作都是他自己做的还是别人帮他做的.(注意:在两个供选择的从句之间若用or字,则须重复whether一字.)注:⑴当强调宾语从句并将其提前时只能用whether。如:WhetherI'llhavetimetogowithyouIamnotsure.我很难说我们是否有时间跟你们一起去。⑵从句作介词宾语时只用whether不用if。如:Shewasundecidedaboutwhethersheshouldaccepthisoffer.她拿不定主意应该不应该接受他的好意⑶当whether和ornot连用时，只用whether不用if。当ornot放在whether引导的从句句尾，则可以用if来替换。如:Idon’tknowwhetherornothewillcome.我不知道他是不是回来。I'llbehappywhether/ifIgetthejobornot我能不能得到那份工作都一样高兴⑷当whether和or连用表示明确的选择时，只用whether不用if。如:HeaskedmewhetherIwantedtogotherebytrainorbybus.他问我是想乘火车还是坐公共汽车去那里。Hehesitatedaboutwhetherheshoulddriveortakethetrain.他开车去还是坐火车去,犹豫不决注:whether和or连用还可以引导让步状语从句,此时也不用if。如：We'llgoonwiththework,whetherwecanfindthenecessarytoolsornot.不管我们能否找到所需的工具,我们要把这件工作做下去。Whetherornotitrains/Whetheritrainsornot,we'replayingfootballonSaturday.无论下不下雨,我们星期六一定踢足球.⑸动词discuss，decide,consider等后习惯上也常用Whether引导从句，不用if。Theydiscussedwhethertheyshouldleaveatonce.他们讨论了是否应该马上离开。Wediscussedwhetherthehouseshouldbesold.我们讨论了这房子是否应卖掉。3.表语从句用whether引导不用if.如:①Thedoubtwaswhetheryouhadbrokenthebeautifulvase.疑问是你是否打坏了这只漂亮的花瓶。4.同位语从句用whether引导不用if.如:①Thequestionwhetherwe'llbuildanotherlecturebuildinghasn'tbeensettled.是否要另建一幢教学楼的问题还未决定。5.在动词不定式之前，只能用whether，不能用if。如:①ThequestioniswhethertogotoMunichorVienna.问题是去慕尼黑还是去维也纳.②Shedoesn'tknowswhethertogetmarriednoworwait.是否现在结婚或是等待她不知道。③Wewerewonderingwhethertogotodayortomorrow.我们弄不清是今天走还是明天走.④I'mnotsurewhethertoresignorstayon.我拿不准主意是辞职还是留任.强化练习：1.Thequestionhasnotbeenanswered____TaiwanwillbeincludedontheOlympictorchrelayroute.A．thatB．whetherC．whichD．if2.Youhavenotyetansweredmyquestion_____Icanjoininthepartytonightornot.A.whetherB.ifC.thatD.which3．—Idliketoinviteyoutoapartythisevening.—Thankyou,but_____I’llbefreeImnotsureatthemoment.A.whileB.ifC.whenD.whether4．---Whatareyouanxiousabout?---___________A.IfwesucceedB.ThatwecansucceedC.DowesucceedD.Whetherwecansucceed5.Onlywhen_____thepainting_____decide______thepaintingisworthbuying.A.hesees,hecan,whetherB.doeshesee,canhe,ifC.hesees,canhe,whetherD.seeshe,hecan,that6._____EnglishishisfavouritesubjectA.IaskedhimifB.IaskedhimthatwhetherC.IaskedhimthatD.Iaskedhimwhich7._____they’llgototheSummerPalace____theweather.A.If;dependsonB.Whether;dependsuponC.Whether;dependedonD.If;dependedupon8.Itisn’tquite___________hewillbepresentatthemeeting.A.sure;whetherB.sure;ifC.certain;whetherD.certain;that9._____the2008OlympicwillbeheldinBeijingisnotknownyet.A.WhetherB.IfC.WheneverD.That10.Noonewassure_____hewouldbeaskedtospeaknextyear.A.whenB.whetherC.whatD.how11.Itisstillaquestiontousall_____thereisanylivingthinginsomeotherplacesinthespace.A.whetherB.whichC.whatD.where12.Idoubt_____hewillcomehereontime.A.thatB.whetherC.whenD.where13.A.butwhetherC.buthow14.“Whatdidheaskyou?”“__A.ThatB.WhenC.Where15.Hetreatedallthepeoplearoundhim,______hekneworhedidn'tknow,______.A.if,friendlyC.if,inafriendlywayD.whether,inafriendlywayA.ifC.thatD.不填Answers:BADDCABCABABADDB