—We don't permit________in our school.Would you please put your cigarette out?

—Forgive me. I didn't know.[ ]

A. to smoking  

B. to smoke  

C. smoking  

D. having smoked

矿井风流在井巷某断面具有的总机械能等于其具有的(静)压能、位能和动能的总和是矿井风流的( )。

A．位压

B．全压

C．动压

D．总压力