单项选择题
A.seal water supply be cut off
B.make-up water supply be cut off
C.oil outlet valve closed or not open sufficiently
D.the flow rate of oil is too much
单项选择题 To ensure oil purifier working in normal condition,the interval between two sludge discharging should not exceed（） hours.
单项选择题 Some refrigeration systems have chemical moisture indicators installed in conjunction with the sight glass in the liquid lineIf excess moisture is present in the system, the indicator will （）
单项选择题 In the navigation, cause the shafting over load most easily（）