---When did you get to know each other ?--It was in we spent summer vocation togeth

问题补充：

---When did you get to know each other ?

----It was in we spent summer vocation together.

A. that

B. when

C. before

D. since

答案：

A. that

(答案→)B. when

C. before

D. since

解析：考查定语从句。先行词为，从句中缺少时间状语所以用关系副词when，句意：你们什么时候开始认识的？就是在我们一起度过暑假的。所以选B。