单项选择题
It is required that ships proceeding at sea should keep continuous watch on（）.
A.VHF channels 16 and 13 B.Appropriate DSC distress and safety frequencies C.INMARSAT TDM message channel D.VHF channel 70 and channel 8
单项选择题 General radio communications in the global system are those between（）concerning the management and operation of the ships and may have impact on their safety.
单项选择题 why do some stations keep silence?（）
单项选择题 What channel is general communication used?（）
