分类：教育/科学-外语学习
问题：英语选择题Havenyouknowneachotherforlo 
Haven you known each other for long?Not very long,________we start to work in this company.A.sinceB.whenC.after答案是A，可为什么另两个不能选？
回答：Haven you known each other for long?
Not very long,________we started to work in this company.
A.since
B.when
C.after

when用于短暂性的动作
用after后就应跟一般现在时
则选择a