一个英文从句逗号后面什么时候用which什么时候用in which呢

which是修饰非限制性定语从句，in which想当于where

in which的in是从which 中抽出来的

就如:
She is the girl whom I want to give a gift to.

但是 we can’t also end a sentence with preposition.

应该是
She is the girl to whom I want to give a gift.

先行词前面却in 后面就要加
不缺，就不用

in which 只能引导的定语从句，而which 则可以引导多种从句，在定语从句中，which在定语从句中可以做主语，宾语，而in which 在定语从句中只能做地点状语。例如：
This is the house which i live in .(做宾语）
This is the house in which i live .(做状语）
要明确which 在这两个句子中都做宾语，我们在考虑时把in which 做为一个整体来想，