单项选择题
A.a needle gun B.soap and water C.a wire brush D.a chipping hammer
Which of the listed chemicals can be routinely used to ...
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 D.Zinc chromate
The ratio of the weight of moisture contained in a give...
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
If a centrifugal pump is driven by a constant speed ele...
单项选择题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
