My father wants to give up       _  , but it’s hard for him to      _   .

A．smoke; give up it

B．smoking; give up it

C．smoking; give it up

D．smoke, give it up

X线胶片对射线对比度的放大能力称为（）

A.相对感度

B.平均斜率

C.胶片对比度

D.照片对比度

E.感光度