When I try to understand ______ that prevents so many Americans from being as happy as one might expect, it seems to me that there are two causes.

A．why it does

B．what it does

C．what it is

D．why it is

手部应清洗消毒后方可接触成品的情况是（）。

A.加工非直接入口食品后，再加工冷菜

B.加工非直接入口食品后，再进行备餐

C.在加工场所进食、饮水或吸烟

D.以上都不是