单项选择题
On a ship，when may a work vest be substituted for a required life preserver?（）
A.To replace a damaged life preserver B.For use during fire drills C.For use during boat drills D.At no time
单项选择题 On a ship，watertight doors should be operated（）.
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（）.
