Cynthia is not ashamed of what  she does, ____ she ends up doing something wrong.    [ ]

A. as though    

B. in case    

C. even if    

D. for fear

在制造齿轮时，有时采用喷丸法（即将金属丸喷射到零件表面上）使齿面得以强化。试分析强化原因。