The radiotelephone message that indicates a station is about to transmit a message concerning the safety of navigation or important meteorological warnings commences with（）.

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.

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?（）.

Which one of the following is the safety signal?（）.A.SS...

单项选择题Which one of the following is the safety signal?（）.