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單項(xiàng)選擇題

Centrifugal pumps, however, can be designed with a number of impellers （） to attain a large amount of liquid.

A.in series
B.in parallel
C.assembled
D.together

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單項(xiàng)選擇題

Sealing in pump shaft is achieved by means of the （）.

A.gasket
B.packing
C.washer
D.spring

單項(xiàng)選擇題

（） is the breakdown of surface tension between oil droplets in an oil water mixture which causes them to join and increase in size.

A.Wear
B.Contaminating
C.Coalescence
D.Coarse separating

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