— Why didn't you stop Mary cheating in the final exam?

— But what _____ otherwise? She just sticks with Alex and turns a deaf ear to my advice. [ ]

A. could I do

B. must I have done

C. could I have done

D. should I do

按产品类别设置检验站，其优点为（）。

A.专业性强

B.熟悉掌握产品结构和性能

C.提高检验效率

D.检测器具统一管理

E.便于交流经验