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表语从句连接词：that/whether/asif/asthough连接代词：who/whom/whose/which/what连接副词：when/where/why/how/because1)that在从句中仅起连接作用，无实际意义，在句中不做任何成分，不能省略。2)whether在表语从句中表是否但不充当句子的成分。if不能引导表语从句.如:1.Whatthedoctorreallydoubtsiswhethermymotherwillrecoverfromtheseriousdiseasesoon.2.Thequestioniswhetheritisworthdoing.3)What在表语从句中充当主语宾语表语，表示什么，什么样子，…的人或事.1.Thequestioniswhatcausedtheaccident.2.Thatmountainisnolongerwhatitusedtobe.3.Whathetoldyouwaswhathadbeendiscussedatthemeeting.4)who在表语从句中充当主语，宾语，表语，表示谁。.1.Theproblemiswhocoulddothework2.Mytroubleiswho(whom)Icanturnto.5)which在引导表语从句时,常充当定语，表语表示哪一个，哪一些。如：Ireadaboutitinsomebookoranother,butwhatIdon’tknowiswhich(book)itis.6)由asif,asthough引导表语从句，表示好像。句子中的系动词常用be,look,appear,seem,sound等。1.Itlooksasifitwasdoingtorain.2.Theyoungmanwithlonghairlooksasifhewereagirl.7)当主句的主语为reason,或者是由why引导的从句时,与它们相关的表语从句用that来引导,而不能由because引导；because引导表语从句时只能用于It/That/Thisis/wasbecause…句型中.1.ThereasonwhyIwaslatewasthatImissedthetrain.2.Iwaslate.It/That/ThiswasbecauseImissedthetrain.注意：当表语从句中主语、宾语、表语具备，但是还是要表示疑问含义，可以判断句子中缺少状语，常常用相应的特殊疑问词引导，有why,when,where,how等Thisishowhedidit.Thatiswhythebrotherswantedtomakeabet.That’swhywe’vegivenyoutheletter.表语从句引导词注意事项1.that引导表语从句时不能省.2.if不能引导表语从句.3.除that外的所有引导词都有自己的意义。4.除that,whether外的所有引导词都须在从句中充当相应的成分