题目内容：

By the time用法可以和when互换么?
两个都能表示“当.”么?

优质解答

by本身有‘.之前’的意思.by the time是典型的要求完成时态的词组,比如：By then,he was 15.那时他已经15岁了.（到那时之前.）By the time she gets there,they will have covered everything.她到那里之前,他们就已...