关于真性红细胞增多症的发病年龄和性别比例正确的是（）

A.多为儿童，男女性别无差异

B.多为中年或老年，女性多于男性

C.多为青壮年男性

D.多为中年或老年，男性多于女性

E.多为青壮年女性

The loading, unloading, transshipment and transit of inward and outward mail bags are subject to Customs control and a ______ wya bill should be submitted to the Customs by the enterprise providing prviding postal service.

A．cover
B．covering
C．covered
D．haveing covered