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單項(xiàng)選擇題

A more sophisticated pressure reducing valve incorporates a pilot valve which controls the fluid above the valve operating piston in response to downstream pressureThe bold and italic word “which” means （）.

A.a pressure reducing valve
B.a pilot valve
C.an operating piston
D.downstream pressure

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單項(xiàng)選擇題

In its simplest form the pressure reducing valve is opened or closed by （） which is balanced by the downstream pressure acting on a diaphragm.

A.adjusting a nut
B.a pre-tensioned spring
C.any spring
D.upstream pressure

單項(xiàng)選擇題

Most marine biological sewage treatment plants consist of all the following statements except （）.

A.aeration tanks
B.settling tanks
C.disinfection agent
D.anaerobic bacteria