介词加which引导的是定语从句，常见的用法有：in which可以翻译成“在……里面”，for which可以翻译成“为了……目的”，on which可以翻译成“在……的上面或具体时间的某一天”，at which可以翻译成“在……里面或在……上面”。
1.in which 在……里面
The school (that/which) he once studied in is very famous.
= The school in which he once studied is very famous.
2.for which 为了……目的
Tomorrow I will bring here a magazine (that/which) you asked for. = Tomorrow I will bring here a magazine for which you asked.
3.on which 在……的上面或具体时间的某一天
I have a dresser in my bedroom, which there are many cosmetics on.
= I have a dresser in my bedroom on which there are many cosmetics.
4.at which 在……里面或在……上面
The dumpling House which he often has dumplings at is very popular.
= The dumpling House is very popular, at which he often has dumplings.