ON WHICH OF WHICH IN WHICH 在定语从句中都咋用

其实你只要搞清楚这些介词在定语从句中与什么动词搭配以及前面的先行词所需的介词搭配即可.
例如：
It was Sunday on which we visited the school.相当于on Sunday
The book,the cover of which is blue,belongs to me.相当于 its cover
The room in which there is a machine is a workshop.相当于in the room.