If you want to start your own photographing company, you’d employ someone who knows _____, which can contribute to the success of your business.      [ ]

A. the tricks of the trade    

B. the trades of the trick  

C. the tricks of trade

D. tricks of the trade

在腰椎侧位X线片上，测量出腰椎分数，正常均值为（）。

A.90%

B.80%

C.70%

D.60%

E.50%