题目内容：

Three days had gone by_I received her e-mail
A.as B.since c.before D.when
选哪个?why?

优质解答

before

追问：

是before，为什么when不行？

追答：

不好意思，一直用的手机，没看见追问，我记得应该是个固定搭配，嘿嘿