Most people believe that ____knowledge is power and that having ____ good command of a

foreign language is of great importance .

A．/ , / ,

B．the , a ,

C．/ , a ,

D． /, the

理论上讲脱氢空速提高后脱氢副反应与所有发生反应的比值将（）。

A.增大

B.降低

C.不变

D.为零