单项选择题
A.insufficient load
B.excessively high oil viscosity
C.relief-valve pressure setting too high
D.reservoir level being maintained two inches above normal
单项选择题 A knocking sound from one cylinder of an operating air compressor indicates （）.
单项选择题 Rotation of the steering wheel on the navigation bridge initiates oil pressure being applied to the steering gear rams by （）.
单项选择题 Which characteristic or condition will have the greatest effect on increasing a hydraulic oils viscosity?（）