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
单项选择题 In a general cargo crane, three principal movements are （）； （）； （）.
单项选择题 A warp end may be fitted for operating the derrick topping wire which adjusts the derrick （）.
单项选择题 These include deck machinery such as mooring equipment, anchor handling equipment, cranes and （）.
