— Did you know any Chinese before you arrived in Beijing?

— Never ________ it, actually.

A．had I learned

B．have I learned

C．I have learned

D．I had learned

赣州市公汽公司为了保证人们从公汽后门上下车时的安全，在无人售票车上安装了“车载电视监控器”．如图所示是该装置的光学系统，图中的摄像头的工作原理相当于______透镜，成______像．