Staring into his eyes, I could see a _______ look in his eyes.

A．puzzle

B．puzzling

C．puzzled

D．puzzley

液压泵将机械能转变为液压油的（）；而液压缸又将这能量转变为工作机构运动的机械能。

A.电能

B.动压能

C.机械能

D.压力能