单项选择题

For occasional heavy loads, two cranes can be arranged to work together. The operating （） for deck crane motors may be hydraulic electric.

A.principle
B.medium
C.instruction
D.voltage

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单项选择题

A.hoisting；luffing；slewing
B.lifting；raising；lowering
C.rotating；raising；handling
D.hosting；lowering；moving

单项选择题

A.length
B.slack
C.height
D.rotation direction

单项选择题

A.boilers
B.bow thrusters
C.stabilizers
D.hatch covers