这要看定语从句的先行词在从句中充当什么成分,充当什么成分就做什么
给你举几个例子看看
1、I still remember the night __when__I first came to the house.
这句话的先行词when就是在从句中充当状语,因为when是修饰the night,在从句中的代表的是 at the night
3、Have you ever been to Hangzhou ,_which___lies the West Lake?
这句话的先行词which在从句中充当的就是主语,因为它修饰的是hangzhou ,从句缺少主语,就有which代表的hangzhou来充当
5、This is the very novel about _which__we've talked so much.
这句话的先行词which在从句中充当的是介词about的宾语
6、He lives in the room ,the window _which__faces to south
这句话的先行词在从句中充当的是主语,即代表the window 做face的主语