單項選擇題

When two oil separators are working in series, they should work with （）

A.both as clarifiers
B.first one as clarifiers, second one as purifier
C.both as purifiers
D.first one as purifier, second one as clarifier

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單項選擇題

Concerning the management of sewage treatment plant using activated sludge, which of the following is correct?（）

A.the plant should be prohibited to supplying air
B.the plant should work at intervals
C.the plant should be added disinfector in time
D.we should check strength of activated sludge, ivory-white color is best

單項選擇題

Disinfector in the sewage biological treatment plant usually is （）

A.chlorine water
B.ozone
C.hypo-calcium chloride
D.calcium oxide