单项选择题
On a ship，watertight doors should be operated（）.
A.during abandon drill B.during fire drill C.weekly D.when the rig is being moved
单项选择题 On a ship，how many ring buoys are required to have a buoyant line attached?（）
单项选择题 On a ship，firefighting equipment must be inspected once every（）.
单项选择题 On a ship，a fixed carbon dioxide or other approved system must be installed（）.
