那是一个信件还是主要沟通方式的年代。
That was a time when letters were the main way people communicated.
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time英 /taɪm/|美 /taɪm/
when英 /wen/|美 /wɛn/
解释
when 引导定语从句修饰 time，定义所指的历史时期。
That was a time when letters were the main way people communicated.
when 引导定语从句修饰 time，定义所指的历史时期。