Question

I'll never forget the day when/which ........什么情况下用when,什么情况下用which?

Answer 1

用which 还是用when主要应该看它们在定语从句中所做的成分， when只能做状语，而 which 主要做主语和宾语。如：
I'll never forget the day (that )we spent together in the summer camp.
I'll never forget the day when I joined the party.

Answer 2

很高兴为您解答：
when引导2个句子，which引导定语从句，which在从句中作主语或者宾语。

祝您学习进步，工作顺心。^_^

Answer 3

什么情况下都不用