1．定语从句
在复合句中，修饰名词、代词或整个句子的从句叫作定语从句。定语从句可以分为限制性定语从句和非限制性定语从句。
The boy who is reading needs the pen which you bought yesterday.那个在阅读的男孩需要你昨天买的钢笔。(定语从句作后置定语)
2．先行词
被定语从句所修饰的词或句子叫先行词，作先行词的可以是：
(1)一个词(通常是名词，也可以是代词)
This is the place which is worth visiting.
这是值得参观的地方。
He laughs best who laughs last.谁笑到最后，谁笑得最好。
(2)一个短语
Many life's problems which were solved by asking family members, friends or colleagues are beyond the capability of the extended family to resolve.许多以前可以通过询问家庭成员、朋友或者同事就能解决的生活问题，是现在的大家庭无力解决的。
