_____, this physics problem seemed    simple, but when I tried to work it out, I   just couldn't.     [ ]

A. On one hand      

B. In my opinion    

C. At first sight      

D. On its own

职业道德作为职业行为准则，有着与其它的（）不具备的特征。

A.社会行为准则

B.职业行为准则

C.工作行为准则

D.社会交往准则