Question

While Mary________as a secretary，her friends were studying at university．

1. A.
   was working
2. B.
   worked
3. C.
   had worked
4. D.
   works

Answer 1

A
分析：表示过去某一段时间里正在进行的动作要用过去进行时。while(在……期间)引出时间状语从句，从句中必须用持续性动词，主句动词study和从句动词work都是延续性动词，可以用时态一致的原则，或者都用过去进行时，或者都用一般过去时。