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．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
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：
