we went through a period ___ communications were very difficult in the rural areas.

问题描述:

we went through a period ___ communications were very difficult in the rural areas.
A.which B.whose C.in which D.with which
为什么选C 不选D
也有 with the period 的说法啊
with the period 也是指时期啊。为什么不能=when

period 时期 后面就应该用when 所以用in which相当于when