单项选择题 A combination combustible gas and oxygen indicator is an instrument that measures the（） of both combustible gas and oxygen; each is indicated on a separate meter.

单项选择题 Deficiencies in the categories of Life-saving, Safety in General, Fire-fighting Appliances and Load Line （） approximately 66% of all deficiencies.

单项选择题 All engineer officers and engine room ratings shall be aware of the serious effects of operational or accidental pollution of the marine environment and shall take all possible（） to prevent such pollution, particularly within the framework of relevant international and port regulations.