We went through a period munications were very difficult in the rural areas.
A. wtach
B. whose
C. in which
D. with which
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A. wtach
B. whose
(答案→)C. in which
D. with which
解析：此题考查定语从句的用法。Period后面的定语从句中缺少时间状语，要用when,而此题中没有when,所以要选择in which相当于in the period,表示时间，作句中的状语。which要在定语从句中作主语或宾语，而此处的“介词+which”中要选择介词in,而不选择with.
定语从句中“介词+which”中介词的选择，一要看先行词，二要看与定语从句谓语动词的搭配，三要看句意。