医用皱纹纸包装的无菌物品，有效灭菌状态可保持：（）.

A.3个月

B.30天

C.6个月

D.一年以上

—What does your father do?  

—He is a        who works in the field on a farm.[ ]

A.teacher    

B.farmer    

C.doctor    

D.driver