—What do you think about the new bag over there?

—Oh, it's ______ empty bag. But it is ______ useful one. [ ]

A. a; a

B. an; a

C. the; the

D. /; a

BTS3001C微基站传输子系统，提供了那些接口。（）

A、E1接口

B、HDSL接口

C、SDH接口

D、ADSL接口

E、HW接口