before 与 until
1. My friends walked me to the bus stop and waited with me _______ the bus arrived. （before ；until ）
此题不能选before，因为时态不对。假如把walked和waited改成过去完毕式had walked和had waited就能够选before。before旳使用一般有强烈旳时态要求而until一般没有时态要求
until
I waited _______ he came back. 我一直等到他回来。
I didn't leave ______ he came back .直到他回来我才走
I can only give you an answer ______ I think it over.
until
until
before