位体积气体中所含粉尘（），称为气体中的粉尘浓度。

A.数量

B.质量

C.重量

which one of the following is not belong to the direct tributaries of inferior vena cava ( )

A．renal veins

B．hepatic veins

C．portal veins

D．lumbar veins

E．common iliac veins