介词+which的定语从句什么时候可以用where,when等替换?

问题描述:

介词+which的定语从句什么时候可以用where,when等替换?
如下面三句能否,why?
This is the town in which they live.
China has a long history during which many of the world's greatest poets were active.
The school in which he once studied is very famous.

简单的说,如果把介词提前的话,就要用介词+which的形式,因为关系副词前面是不能加介词的.就像第一句和第三句live和studies的介词in如果放在一起,前面就能用where,this is the town where they live inthe school wher...