定语从句：用一句话给名词"加戏"

"那个穿红衣服的女孩是我妹妹"，想写复杂点可以说 The girl who is wearing red is my sister。后面那句就是定语从句。

基本结构

先行词（名词）+ 关系代词 + 从句

• The man who lives next door is a doctor.
• This is the book which I bought yesterday.

关系代词怎么选

指人：who / that

• The boy who won the prize is my cousin.

指物：which / that

• The book which is on the desk is mine.

所属：whose

• I know the boy whose father is a teacher.

做宾语可省，做主语不能省

• This is the book (which) I bought.（which 是宾语，能省）
• The man who lives next door is a doctor.（who 是主语，不能省）

别重复

关系代词已经代替了先行词，后面别再带出代词：

• 错：This is the book which I bought it.
• 对：This is the book which I bought.

口诀：人 who 物 which，所属用 whose；主别省宾可省，后面别再加代词。