1、只用which不用that的情況。
2、引導非限制性定語從句時。例如:Bamboo is hollow, which makes it light.竹子是空心的,這使得他很輕。
3、當關系詞前有介詞時。例如:This is the room in which Chairman Mao once lived.這就是毛主席曾經住過的地方。
4、在一個句子中有兩個定語從句,其中一個定語從句的關係代詞用了that,另一個宜用which.例如:Let me show you the novel that I borrowed from the library which was newly open to us.我來給你看我從新開的圖書館裏借來的那本小説。
5、當關系代詞後面有插入語時。例如:Here is the English grammar which, as I have told you, will help improve your English.這就是我跟你説過的會有助於你學好英語的那本英語語法書。
6、先行詞為that時。例如:The clock is that which can tell us the time.鍾是報時的裝置。