I、基本概念
1、什么叫定语：修饰名词、代词的形容词、分词、介词短语或句子叫定语。
e.g. an old film, a broken window, a sleeping boy, the plane in the sky,
2、什么叫定语从句？
修饰一个名词或代词的句子叫定语从句。
e.g. the boy who helped me yesterday, those who want to go home on Sunday
the book that she bought yesterday, the factory which makes tools
3、什么叫先行词？
被定语从句修饰的名词或代词叫先行词。先行词前一般用“the” ，但在指“一个”概念时，用 “a , an ”。
e.g. A plane is a machine that can fly. He is the boy who can do it alone.
4、什么叫关系代词、关系副词？
连接先行词和定语从句的词叫关系代词、关系副词。
e.g. the boy who helped me yesterday, those who want to go home on Sunday
book that she bought yesterday, the factory which makes tools
