—Who is the volunteer for Exp0 2010 Shanghai China?            

—I think it __   __ your sister. Because she likes volunteering.               [ ]

A. can't be            

B. must be            

C. wouldn't be

缝焊用的电极是（）的滚盘。

A.圆形

B.长方形

C.正方形

D.菱形