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?（）
单项选择题 Crude oil washing of cargo tanks has the following advantages except for （）
单项选择题 Where is the cooling water from the compensating tank in the cooling water system of main engine lead to?（）
