____ in the United States, St Louis has now become the 4^th largest city.

A．It is the 24^th biggest city

B．It was the 24^th biggest city

C．Before the 24^th biggest city

D．Once the 24^th biggest city

统计机构、统计人员对在统计调查中知悉的统计调查对象的（），负有保密义务。

A.单项调查资料

B.综合统计资料

C.基本统计资料

D.商业秘密