— I haven't got the reference book yet, but I'll have a test on the subject next month.

— Don't worry. You _____ have it by Friday. [ ]

A. could

B. shall

C. must

D. may

用总流能量方程时，上、下游两过流断面的压强( )。

A．必须用绝对压强

B．必须用相对压强

C．必须用相对压强水头

D．相对压强和绝对压强均可用，但等号前后应统一使用同一种压强