导读：定语从句的概念，在复合句中，修饰某一名词或代词的从句叫定语从句。
例如： 1) The man who lives next to us is a fool.
2) You must buy me the house which is near Xiangshan.
上面两句中的the man和the house是定语从句所修饰的词，叫先行词，定语从句放在先行词的.后面。
关系词(连接词)
1.关系代词引导的定语从句
引导定语从句的关系词有关系代词：that, which, who 和关系副词where, when, why。关系词放在先行词和定语从句之间，起连接作用，同时还做定语从句的一个成分。
2.关于that, which的用法注意点
1)只能用that，不用which作为定语从句关系代词的情况
a)不定代词，如anything, nothing, the one, all, much, few, any, little等作先行词
There is nothing that I can do.
I mean the one that was bought yesterday.
b)先行词有the only, the very, the same, the last修饰
This is the very book that I want to find.
The last place that I visited was the hospital.
c)先行词为序数词、数词、形容词最高级时