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單項選擇題

（）is not installed on the emergency switchboard.

A.Control panel
B.Paralleling panel
C.Load panel
D.Busbar

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單項選擇題

（）can be used to prevent hydraulic system overloaded or keep the pressure of oil outlet from pump constant.

A.Overflow valve
B.Reducing valve
C.Balancing valve
D.Reducing valve or balancing valve

單項選擇題

The symbol (GB786√1-93) at right side represents （）

A.overflow valve
B.reducing valve
C.relief valve
D.sequence valve