—I'm terribly sorry to interrupt, but may I use your phone? It's rather urgent.

—Yes,      . [ ]

A.  with pleasure            

B.  no burry        

C.  it doesn't matter          

D.  of course

使磨矿工艺指标升高的因素是（）。

A、给矿量降低

B、可磨度系数变小

C、原矿粒度变小

D、磨矿浓度变小