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單項選擇題

（） play a very important part in hydraulic systems by preventing interaction between different parts of the hydraulic circuit.

A.Motors
B.Check valves
C.Safety valves
D.Reducing valve

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單項選擇題

Cargo handling unit is rated according to the （） to be lifted.

A.cargo crane
B.jib
C.safe working load
D.oil pressure

單項選擇題

When the union purchase derrick is operated, one derrick is positioned over the quayside and the other almost vertically over the （）.

A.dock
B.hold
C.pedestal
D.machinery space

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