We often think of the days__we spent together on island.
问题描述：
We often think of the days__we spent together on island.
A.when
B.which
C.in which
D.during whic 为什么不选D
答
we spent together on island.是定语从句,spent 是及物动词,需要宾语the days,即spent the days together...,故the days 后面需要用关系代词which（代替the days）来作spent的宾语.
而during which则是时间状语,定语从句需要的是宾语,不是状语.