-- Which floor does John live on?

-- He lives on the __________floor of the building.

A．five

B．fifth

C．fifteen

D．fifty

细菌分离首选的培养基是( )。

A．营养肉汤

B．营养琼脂培养基

C．血清琼脂培养基

D．血液琼脂培养基

E．麦康凯琼脂培养基