此句in which 引导的事定语从句吗?

问题描述:

此句in which 引导的事定语从句吗?
The united state of America is often seen as a nation in which the pursuit of happiness is not a dream but a reality.

基本学定语从句的娃就一定会死在这里.in/at which=where,也就是说the United States of America is often seen as a nation where the pursuit of happiness is not a dream but a reality.就是美国被看做这样一个国...此句介词in可以换成别的介词吗?为什么?这句不能换成别的介词,学东西不要那么死,我只是举例子,有些时候可以换成at,你根本没搞懂我上面说的.介词会用吗?你可以说成at USA吗?当然不可以了.只能用in USA.自己多找些定语丛句的资料看吧