單項(xiàng)選擇題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
D.Zinc chromate
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1.單項(xiàng)選擇題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
2.單項(xiàng)選擇題If a centrifugal pump is driven by a constant speed electric motor and produces a discharge pressure less than designed, the cause is probably（）.
A.excessive pump speed
B.excessive suction head
C.worn wearing rings
D.gross pump misalignment
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