问下in which是不是=where,at which是不是=when,for which是不是=why呀?

where 可以引导所有类型的从句,只有在它引导定语从句时 才可能
和in which 替换,其他时候都不行.这取决于先行词与介词的搭配：
This is the village where / in which I was born.
This is the village where / from which he joined the army.
This is the shool gate where / at which we met the other day.
I was born in the village.
He joined the army from the village.
We met at the school gate the other day.
at which是不是=when：是否选择when还是使用at which是有效性错误的问题,时态才是关键,
但是日常做题目的时候可以这样理解这个考点：时间状语后面比如year,age,通常用when修饰,但是 介词+which的修饰更优,往往更清晰.
for which是不是=why：很抱歉 我没查到他们的区别 而我自己又认为他们没什么区别 他们可以互换
why是关系副词 ,而for which 是介词＋which结构
关系副词含义相当于＂介词＋which结构＂,因此常常和＂介词＋which＂结构互换
其中
关系副词有：when,where ,why
介词＋which结构有：
when =in/on which ,where=in/at which ,why =for which
对了 是在定语从句中的...