单项选择题
（） can be operated independently or locked together and operated as a twin-job cranes of double capacity.
A.Two derricks
B.A derrick and a crane
C.Two cranes
D.A crane and a winch
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相关考题
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单项选择题
Some cranes are mounted in pairs on a common platform which can be rotated through（）.
A.360°
B.270°
C.180°
D.90° -
单项选择题
Deck cranes require（） time to prepare for working cargo than derricks.
A.less
B.more
C.many
D.much -
单项选择题
The duty of a deck winch is to lift and lower a load by means of a fixed rope on （）.
A.a warp end
B.a mooring winch
C.a worm gear
D.a barrel
