— There'ssomeone knocking on the door. Who _____it be?

— It must be Mary. She promised to be here at 8：00.

A．must

B．need

C．shall

D．Can

对于近视眼患者来说，远处物体所形成的物像落到[ ]

A．视网膜的前方          

B．视网膜的后方    

C．视网膜上              

D．不一定