单项选择题
The packing installed in the pump stuffing box is lubricated by （）.
A.gravity and feed oil cups
B.grease cups
C.hand during installation
D.leakage through the stuffing box
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The steam coils in a high pressure evaporator used for saltwater service should be de-scaled with （）.
A.a needle gun
B.soap and water
C.a wire brush
D.a chipping hammer -
单项选择题
Which of the listed chemicals can be routinely used to maintain the hygienic quality of potable water?（）
A.Hydrochloric acid
B.Chlorine
C.Sulfuric acid
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单项选择题
The ratio of the weight of moisture contained in a given volume of air, to the weight of moisture that the same sample would hold if saturated, is called the（）.
A.absolute humidity
B.relative humidity
C.specific humidity
D.total humidity
