单项选择题
One of the reasons that cause oil flowed from sludge outlet of a self-cleaning separator is（）
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 oily water is too much
单项选择题 When two oil separators are working in series, they should work with （）
单项选择题 Concerning the management of sewage treatment plant using activated sludge, which of the following is correct?（）
单项选择题 Disinfector in the sewage biological treatment plant usually is （）
