单项选择题
Which of the substances listed is satisfactorily removed from the fuel by a centrifugal oil purifier?（）
A.Impurities B.Lube oil C.Gasoline D.Diesel fuel
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 （）.
单项选择题 The pH value of water in a diesel engine closed cooling water system should be maintained between （）.
