— There's somebody at the door. Who _____ it be? Is it the postman?

— No. It _____ be him. It's just seven o'clock. It's too early.

                  [ ]

A. may; can't         

B. will; won't        

C. may; mustn't

汽车前进通过侧滑试验出的侧滑板时，若转向内滑说明（）。

A.前束值过大

B.前束值过小

C.前束值合适

D.前束值不确定