Question

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

Answer 1

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。

Answer 2

A when
when指代的是一段时间
你在荒岛上共度的是一段时间

Answer 3

B 关系代词在从句中做宾语。

Answer 4

选B
此句为宾语从句，the days 是先行词，在从句中做spent的宾语，spent是及物动词，故选择B