--Have you seen ____Audi car I parked here?

---Is it _____ black one? A young man has driven it away.

A．an, a

B．the, the

C．the, a

D．an, the

当液体的蒸发速度与气体冷凝速度相等时气体和液体达到平衡，此时的气体称为（）。

A.饱和蒸汽

B.过热蒸汽

C.不饱和蒸汽

D.低压蒸汽