单项选择题
What is the function of wearing rings found on some centrifugal pumps? （）
A.Absorb erosion of high velocity discharge stream B.Seal pump shaft against entry of air C.Isolate the outlet side from the inlet side D.Dampen the turbulent discharge flow
单项选择题 What is the best indication of the loading of a diesel engine?（）
单项选择题 What is NOT a responsibility of the tankerman in charge of loading an unmanned tank barge? （）
单项选择题 What is NOT a precaution to be taken when topping off? （）
