---- I’ll be able to come to see your performance at 8:30 tomorrow evening.

---I’m sorry, by then my performance____ and I___ reporters in the meeting room.

A．will be ended; will meet

B．is to end; will meet

C．will have ended; will be meeting

D．will be ended; am going to meet

在关系数据库中，实现“表中任意两行不能相同”的约束是靠______。

A．外码

B．属性

C．主码

D．列