单项选择题
What is NOT a distress signal?（）
A.A continuous sounding of the fog horn B.Firing a gun every minute C.Five or more short rapid blasts on the whistle D.A square flag and ball flown from the mast
单项选择题 The service life of distress signals must be not more than（）.
单项选择题 The radiotelegraph alarm signal may be used to announce（）.
单项选择题 The distress message of a ship should include considerable information which might facilitate the rescue. This information should（）.
