为什么有些句子只能用inwhat不用inwhich

Question

为什么有些句子只能用in what 不用 in which

Answer 1

in which常在定语从句中出现.
如:The house in which we had lived for ages was destroyed
in the flood.
此句中的in which 就是定从.修饰 the house.in which=where
in what 一般会在名词性从句中出现.
如:I am quite interested in what you want for your birthday.
what you want for your birthday为in的宾语.