When I try to understand ______ that prevents so many Americans from being as happy as one might expect,

it seemed to me that there are two causes. [      ]

A. why it does

B. what it does

C. what it is

D. why it is

（）从事消防监督检查的人员应当经过消防业务培训合格后上岗。

A、公安派出所

B、党政机关

C、企业、事业单位

D、消防中介组织