时间或条件状语从句不能用将来时态

时间或条件状语从句不能用将来时态
 
由when, as soon as, before, after, as, until等引导的时间状语从句以及由if, unless, as long as, in case等引导的条件状语从句不能直接用将来时态，遇此情况英语习惯上用一般现在时代替一般将来时。如：
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误：Do it before you will forget.
正：Do it before you forget.
我到达那儿后就给你写信。
误：I’ll write to you after I will get there.
正：I’ll write to you after I get there.
如果他来，请告诉我一声。
误：In case he will come, let me know.
正：In case he comes, let me know.