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單項(xiàng)選擇題

A deepwell pump is a type of（）.

A.screw pump
B.centrifugal pump
C.eductor
D.gear pump

單項(xiàng)選擇題

A definite advantage of using water as a fire extiguishing agent is its characteristic of（）.

A.alternate expansion and contraction as water in a liquid state becomes a vapor
B.absorption of smoke and gases as water is converted from a liquid to a vapor
C.rapid contraction as water is converted from a liquid to a vapor
D.rapid expansion as water absorbs heat and changes to steam