谈定语从句中的关系代词可换与不可换请看下面这道选择题：Ihavetoldeverything________Iknowtoyou．A．whatB．thatC．whichD．who本题考查的是定语从句关系代词的用法。关系代词that，which和who引导定语从句时，在句中的职能和意义彼此相通：即which用来指物，who用来指人，that即可指物，也可指人。指物时，which和that有时可以互换；指人时，who和that有时可以互换，但在下列情况下却不能互换：1．如果定语从句所修饰的词是指物的不定代词时，用that不用which。故此，本题答案应选B（that），不选C（which）。也就是说，在本题中，that与which不能互换。但是指人的不定代词用that或who皆可。例如：Theywillpunish（惩罚）anybodythat／whocutdownyoungtrees．2．当定语从句所修饰的词有限定的修饰词时，必须用which或who，不能用that。例如：（1）April1stisthedaywhichiscalledAprilFool'sDayinthewest．(2)Iknowthedetectivewhosuccessfullysavedthelittleboyintheaccident．3．当定语从句所修饰的那个词是数词或所修饰的那个名词有一个数词作定语时，一般用that，不用which。例如：ThetwobooksthatIboughtyesterdayareEnglishnovels．4．在only，no，any，little，much，all之后，以及先行词带有最高级修饰语时，一般多用that不用which，但all指人时，用who不用that。例如：(1)Thisistheonlybookthatwecanborrow．（2）ThatisthebestfilmthatIhaveseensofar．（3）Thebookcontainsmuch／littlethatisuseful．（4）Allwhoknowhimlikehimverymuch．（5）Sayallthatyouknow．5．that不能像which，whom那样放在介词之后，而必须将介词调到句末。例如：（1）Themanthat／whoyoutalkedwithyesterdayismyuncle．或Themanwithwhomyoutalkedyesterdayismyuncle．（2）ThisisthecageinwhichPollylives．或Thisisthecagethat／whichPollylivesin．6．人和物并列作先行词时，在thesame，thevery，thelast和序数词之后时，常用that，一般不用which或who。例如：（1）Shewasthefirst／thelaststudentsthatcamethismorning．（2）HemadeaspeechonthemenandthingsthathehadseeninCanada．(3)Lookingatthemanandhisdonkeythatarewalkingupthestreet．(4)ThisisthesamepenthatIlostyesterday．（5）ThisistheverybookthatIhavebeenlookingfor．7．前面有who，which，what等疑问代词时，定语从句的关系代词应用that，不用who或which。例如：（1）Whoisthemanthatisstandingbythedoor？（2）Whothathassuchahomedoesnotloveit？（3）Whichisthedogthatyoulostyesterday？（4）Whatthatyousaydoesnotinteresthim？8．先行词为that，those指物时，关系代词用which。those指人时，关系代词用who，that皆可。例如：（1）Pleaseshowmethatwhichyouboughtyesterday．（2）Thatwhichyouborrowedfrommewasn'tarealdiamondnecklace．（3）Theyarethosewho／thatwelove．