3. 定语从句有时不直接紧靠先行词，中间由一个定语、状语或谓语隔开。
e.g. There is an expression in his eyes that I can’t understand.
4. 引导定语从句的关系副词有时可以用“介词 + which”来代替。
e.g. October 1, 1949 was the day on which ( = when ) the People’s Republic of China was founded.
5. 当定语从句中谓语动词是带介词或副词的固定短语动词时，短语动词的各个固定部分不要拆开。
e.g. The sick man whom she is looking after is her father.
6. 介词在关系代词前，只能用which和whom，且不能省略；介词在句尾，关系代词可有which, that, whom, 口语中也可用who，且可省略。
e.g. The man (whom/ who/ that) you were talking about has come to school.