日常人们所说的废水，按其产生的来源，一般可分为（）三种。
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测定废水中有机污染物数量的指标，目前常用的有（）和（）两种。前者用BOD来表，后者用COD来表示。
污水处理的一级排放标准要求，CODcr≤（），SS≤（），PH=（）。
According to this passage, which of the following statements is true？
A. In boiler and machinery spaces, there is the air conditioning.
B. In the boiler rooms the requirement of air volume should meet 25-50% of combustion requirement.
C. To maintain the comfort zone in the separate control room the air conditioning plant should be fitted.
D. The comfort conditions can be maintained in the engine room all the time.
At the middle pressure and large air quantity,_________ is more suitable.
A. an axial flow fan
B. a radial flow blower
C. a centrifugal fan
D. an auxiliary blower
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