To keep the air clean, this hospital _____ all the patients ____ in and around it.

A．allows; smoking

B．forbids; to smoke

C．prevents; smoke

D．prohibits; smoke

氧气桶内压力降低到多少时即不可使用（　　）

A．3kg/cm2

B．5kg/cm2

C．7kg/cm2

D．10kg/cm2