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單項(xiàng)選擇題

In a general cargo crane, （） is fitted to raise or lower the jib.

A.the slewing motor
B.the luffing motor
C.the hoisting motor
D.none of the above

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單項(xiàng)選擇題

External and internal leakage in hydraulic systems may be caused by （）.

A.unusual vibration
B.excessive worn parts
C.abnormal pressure
D.any of the above

單項(xiàng)選擇題

What type of valve is used to direct the flow of hydraulic fluid?（）

A.Relief valve
B.Direction control valve
C.Stop valve
D.Pressure control valve