单项选择题
A.MAYDAY B.PAN-PAN C.SECURITE D.SOS
The radiotelephone message that indicates a station is ...
单项选择题The radiotelephone message that indicates a station is about to transmit a message concerning the safety of navigation or important meteorological warnings commences with（）.
A.TTT B.The spoken word PAN C.The spoken word SECURITE D.XXX
The Urgency Signal（）indicates that the station calling ...
单项选择题The Urgency Signal（）indicates that the station calling has a very urgent message to transmit concerning the safety of a ship or aircraft，or of some person on board or within sight.
A.SOS B.XXX C.TTT D.PAN
Which of the following indicates a grave and imminent d...
单项选择题Which of the following indicates a grave and imminent danger requesting immediate assistance on radio telephone?（）.
A.SOS B.Mayday C.Securite D.PAN
