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
单项选择题 Which one of three elements for a fire on a tanker vessel is most difficult to eliminate (isolate)?（）
单项选择题 Which system(s) in the hydraulic systems of crane always hold(s) single side of load?（）
单项选择题 Crude oil washing of cargo tanks has the following advantages except for （）
