单项选择题 Where shall the key to C02 room be kept?（）

单项选择题 Your vessel is crossing a narrow channel.A vessel to port is within the channel and crossing your course.She is showing a black cylinder.What is your responsibility?（）

单项选择题 The disinfection of various compartments in a vessel by filling with a gaseous agent to destroy rats and all insects pests which act as germ carriers means（）.