China's grain production has been on _______ rise in the past eight years, with _______ annual increase of 17.5 billion kg. [ ]

A. the; an          

B. a; an          

C. the; the          

D. a; the

（）不属于杀毒软件作用之一。

A.检测计算机是否感染病毒

B.清除计算机感染病毒

C.对病毒入侵产生保护

D.进行软件评估和升级