A.lower condensingB.higher coolingC.lower coolingD.high……

单项选择题Before the sludge in a purifier is ejected,（）

A.the oil feeding is stopped and replaced by admitting flushing water
B.the flushing water feeding is stopped and replaced by admitting oil
C.the feeding of dirty oil and flushing water is stopped
D.the feeding of dirty oil and flushing water is admitted

单项选择题A centrifuge of which the bowl is arranged as the upper and lower parts separate discharges the sludge（）

A.by opening the separator manually
B.by separating the lower part from the upper part automatically
C.by separating the upper part from the lower part automatically
D.continuously

单项选择题“A centrifuge consists of an electric motor driving a vertical shaft on the top of which is mounted the bowl assembly”.According to this sentence, we can know that is mounted on the top of the vertical shaft（）

A.a centrifuge
B.an electric motor
C.a bowl assembly
D.a driving motor

单项选择题The treatment of the fuel oils involves storage, heating, filtering and（）

A.centrifuging
B.pressurizing
C.atomization
D.igniting

单项选择题When anaerobic bacteria convert the sewage to an inert sludge,（）

A.no oxygen is needed
B.oxygen is necessary
C.oxygen is given off
D.no gas is produced