in which=where,那什么which等于when?还有什么of which=什么?

定语从句中,有时where、when等可以与介词+which结构相互替换：
介词的使用是根据先行词而言的.
例如：I'll go to the park where I can fly a kite.我将去公园,在那里我可以放风筝.此处where=in which,因为in the park.
I‘ll go to the station where I'll pick up my brother.我将去车站,在那里我将接我的弟弟.此处where=at which,因为at the station.
至于when的情况,也是看先行词：
例句：It was five o’clock at which I was doing my work.那时候是五点,我正在工作.
It was Sunday on which I had a picnic.那是一个周日,我们去野餐了.
of which是指与先行词是从属关系.
例句：I have some friends ,of which Tom is the best one.
并不是所以情况下都可以和介词+which结构相替换,得看where,when等疑问词是否能在不引起歧义的情况下表达出相应的含义.