---Can i make a reservation for tommorrow's concert?

问题描述:

---Can i make a reservation for tommorrow's concert?
----Sorry,all the seats_____by 9:00 this morning.
A.had been reserved B.were reserved C.have been reserved D.would be reserved

by 9:00 this morning.
有by啊,这一般是完成时的标志啊,你要理解这句话的意思.做多了题的话就会懂的.