after/before+从句/doing例句

after 和before 引导时间状语从句时具体用法
before 所引导的时间状语从句 所表示的动作 发生在主句动作之后 如果强调主句的动作发生在前 主句谓语 要用过去完成时 before 引导的从句用一般过去时 如不强调动作的先后 主句和从句 均用一般过去时
如 she worked in shsnghai before she came here.
she had studied english for six years before she went to college
另外注意 before 所引导的时间状语从句 常表示 。。。之后 才。。
如果主句 是一般将来时 从句用一般现在时
如 it won't be long before we meet. again 不久我们就会再见面
after所引导的时间状语从句 所表示的动作 发生在主句动作之前 如果强调从句的动作发生在前 从句谓语 要用过去完成时 主句用一般过去时 如不强调动作的先后 主句和从句 均用一般过去时
如 after he did his homework, he went to bed
after she had waited for him for an hour ,she started for home.
主句是 一般将来时 after 从句用 一般现在时或现在完成时 代替将来完成时
如 i 'll write to you after i finish / have finished my work