They ____ on the program for almost one week before I joined   them,and now we ____ on it but 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

以下有关铁的变化，属于物理变化的是（　　）

A．铁丝燃烧

B．铁器生锈

C．铁杵磨成针

D．铁矿石炼铁