单项选择题
A.position will automatically be sent
B.position will only be sent if the vessel is making a distress call
C.MMSI will indicate its ocean region
D.None of the above
单项选择题 When can routine communications be resumed when radio silence has been imposed?（）
单项选择题 When can routine communications be resumed on a frequency or channel on which radio silence has been imposed? （）
单项选择题 When a vessel signals her distress by means of a gun or other explosive signal，the firing should be at intervals of approximately（）.