They _______ on the program for almost one week before I joined them,and now we _______ it as no good results have come out so far.

A．had been working; are still working

B．had worked; were still working

C．have been working; have worked

D．have worked; are still working

He did well in the examination. He _____ hard at his lessons..  

A．must have worked

B．can have worked

C．will have worked

D．has worked