单项选择题
A lube oil filter can be used to remove most contaminants from lube oilA contaminant which will remain in the lube oil after filtering is （）.
A.acid B.fuel oil C.sediment D.water
单项选择题 Which pump installation would require an external source of sealing water?（）
单项选择题 The accumulation of air and other non-condensable gases in a refrigeration system will （）.
单项选择题 Pressure in an operating hydraulic system is developed （）.
