He, an average citizen, always thinks of_____ he can do more for the people. [ ]

A. how            

B. why          

C. what            

D. which

滚压加工对材料的滚压次数不能超过2次，否则产生（）现象。

A.加工硬化

B.塑性变形

C.脱皮

D.断裂