单项选择题
A magnetic strainer is used in the diesel engine reduction gear oil system to remove small particles of（）.
A.water B.babbitt C.iron or steel D.acids
单项选择题 Which of the substances listed is satisfactorily removed from the fuel by a centrifugal oil purifier?（）
单项选择题 The most common contaminate of governor hydraulic fluid is （）.
单项选择题 The purpose of the safety relief valves installed on an auxiliary boiler is to （）.
