问题补充：
------Have you known each other for long?
------ Not very, we started to work in the ABC Motor Company.
A. before
B. since
C. when
D. after
答案：
A. before
(答案→)B. since
C. when
D. after
解析：考查介词，before 意思“在…之前”，since意思“自从”，when意思“当什么时候”，after意思“在…之后”，句子意思“自从我们开始在美国汽车公司”，所以选B
