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單項(xiàng)選擇題

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

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單項(xiàng)選擇題

Which of the following indicates a grave and imminent danger requesting immediate assistance on radio telephone?（）.

A.SOS
B.Mayday
C.Securite
D.PAN

單項(xiàng)選擇題

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

A.SSS
B.TTT
C.XXX
D.FFF

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