We went through a period_____ communications were very difficult in the rural areas

in
which介词加
关系代词
，相当于when
定语从句
是communications
were
very
difficult

in
the
rural
areas

我们经历了这样的一个时期，在那个时期中通信在乡村是非常困难的

C

个人觉得选C是因为a
period,in
which就是说
in
a
period
wo
went
through.

我们度过了/经历了一个时期，在这时期中，在那个乡村很难沟通。