用来说明主句中某一名词或代词（有时也可说明整个主句或主句中一部分）而起定语作用的句子叫作定语从句。
一、关系代词引导的定语从句
1. 关系代词用来指代先行词是人或物的.名词或代词
句子成分 用于限制从句或非限制性从句 只用于限制性从句
代替人 代替物 代替人或物
主语 Who which that
主语 Whom which that
宾语 Whose（=of whom） whose（=of which）
例1：This is the detective who came from London.
例2：The book which I am reading is written by Tomas Hardy.
例3：The desk whose leg is broken is very old.
例4：This is the room that Shakespeare was born in.
2.关系代词的用法
（1）如果先行词是all，much，anything，something，nothing，everything，little，none等不定代词，关系代词一般只用that，不用which.例如：
All the people that are present burst into tears.
