问题描述：
状语从句中 什么时候用since 什么时候用before?就比方说 it was half
状语从句中 什么时候用since 什么时候用before?就比方说 it was half a year _ ___my good friend returned to his hometown.为什么填before而非since
状语从句中 什么时候用since 什么时候用before?就比方说 it was half a year _ ___my good friend returned to his hometown.为什么填before而非since
问题解答：
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