定语从句【区别】限制性定语从句对先行词起修饰作用（相称于形容词的作用，他的作用一是放在先行词与定语从句中间起了连接作用,二是在从句中担当一种成分，并与先行词保持数的一致。）非限制性定语从句对先行词起补充阐明作用，先行词与定语从句往往用逗号隔开，句子相称于并列句，状语从句.一、关系代词分类用于限制性和非限制性定语从句用于限制性定语从句非限制性定语从句关系代词与关系副词的使用方法：指人指物既指人又指物1、关系代词和关系代词在任何条件下都不能省略。主格词Who 不可省Which That 不可省2、Who whom which 不能用 that 替代也不能互相替代。宾格词Who（m） 可省3、在“介词+Which/Whom”从句的构造中介词不能移到从句背面。属格词Whose/of whom 不可省Whose/of which 不可省Whose 不可省4、when where 可以用于非限制定语从句中。一、关系代词使用方法That（限制定语从句中必须用的几种状况）1、当先行词是不定代词 all，much,little，something,everything，anything，nothing，none,the one 时。例:He told me everything that he knows.2、当先行词被 the only，the very，any,few，little，no，all 修饰时。例：All the books that you offered has been given out.3、当先行词是形容词最高级或先行词的前面有形容词的最高级修饰时。例：This is the best book that I have ever read.4、当先行词是序数词或前面有序数词修饰时。例:We talked about the persons and things that we remembered。5、当先行词即有人又有物时。例：They talked about the teachers and the schools that they knew.6、当主句的主语是疑问词 who 、which 时。例：Who is the man that is making a speech?7、有两个定语从句时，其中一种用了 which 此外一种宜用 that.例：Edison built up a factory which produced things that had never been seen before8、当先行词在主句中作表语,而关系代词在从句中作表语时.例：China is not the country that it was。9、当要避免与疑问词 which 反复时例：Which is the car that was made in Beijing？10.主句是 There be 构造，修饰物，充当主语的定语从句宜用 that 作关系代词.（备注：在 There be 构造中,修饰人，充当主语的定语从句宜用关系代词 who 指代人例：Th...
