She will tell us why she feels so strongly that each of us has a role _______ in making the earth a better place to live on. [ ]

A. to have played   

B. to play     

C. to be played    

D. to be playing

电动扳手根据螺帽大小选择匹配的（），并妥善安装。

A.套筒

B.螺栓

C.螺丝

D.承力杆