一道英语高考语法题（定从）We went through a period ___ communications were very difficult in the rural areas.空白处应是 in which ,为什么不能是which?

一道英语高考语法题（定从）We went through a period ___ communications were very difficult in the rural areas.空白处应是 in which ,为什么不能是which?
一道英语高考语法题（定从）
We went through a period ___ communications were very difficult in the rural areas.
空白处应是 in which ,为什么不能是which?

一道英语高考语法题（定从）We went through a period ___ communications were very difficult in the rural areas.空白处应是 in which ,为什么不能是which?
关键是看空白处加入的引导词在从句中做什么成份.
从句communications were very difficult in the rural areas已经是一个完整的句子了.所以,只能加状语.如果用which,就是引领宾语从句,而从句中不缺宾语.从句中中缺一个时间状语,所以用in which或when来引导.