–Hi, Tom, You look tired.

--Yes, I _____________ the room all the afternoon.

A．painted

B．had painted

C．have painted

D．have been painting

雷达辐射监视器图形变坏，则可认为（）。

A、混频晶体性能减退

B、磁控管电流减少

C、波导或天线有故障

D、以上都是