单项选择题
Which condition is necessary for a substance to burn?（）
A.The temperature of the substance must be equal to or above its fire point B.The air must contain oxygen in sufficient quantity C.The mixture of vapors with air must be within the explosive range D.All of the above
单项选择题 When retrieving the survival craft，the winch operator should stop the winch and check（）.
单项选择题 When jumping into water upon which there is an oil-fire，you should（）.
单项选择题 When joining a vessel，do not forget personal documents and your spectacles，and（）if necessary.
