C
这是个定语从句的问题
look forward to doing/sth.
所以这个从句里不缺介词
直接用which代the day就可以了为什么不用when呢？我给你举个例子吧where和when都是关系副词，which是关系代词，in which可以理解为where/when用where举例：This is the house where I live.This is the house which I live in.=This is the house in which I live.这里面就是有没有in这个介词的差别有了where就不加in,which就要加，也可以说in which=wherewhen和where的用法是一样的原句中，look forward to sth.不缺介词to，所以用which