It won't be long before you regret what you've done.

问题描述:

It won't be long before you regret what you've done.
It won't be long (before) you regret what you've done.
A.after B.before
C.since D.when
为什么是before?

译文为“过不了多久你就会为你的所作所为后悔”.
...long before...是比较固定的搭配,其他三项都不符合题意,而且after一般用在过去式中,since一般用于完成式