单项选择题

The crane jib is raised and lowered by means of （）

A.a mooring winch
B.a hoisting winch
C.a slewing winch
D.a luffing winch

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单项选择题

Which one of three elements for a fire on a tanker vessel is most difficult to eliminate (isolate)?（）

A.a combustible element, fuel
B.energy (resources for ignition) to start the combustion
C.oxygen to support the combustion
D.both A and C are correct

单项选择题

Which system(s) in the hydraulic systems of crane always hold(s) single side of load?（）

A.hoisting system only
B.hoisting system and luffing system
C.hoisting system and slew and slewing system
D.slewing system only

单项选择题

Crude oil washing of cargo tanks has the following advantages except for （）

A.reducing the erosion of the cargo tanks
B.increasing the total quantity of oil to carry
C.reducing the quantity of water contained in oil
D.reducing cargo discharged time