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單項(xiàng)選擇題

The radiotelephone safety message urgently concerned with safety of a person would be prefixed by the word（）.

A.Mayday
B.Pan
C.Safety
D.Interco

單項(xiàng)選擇題

The radiotelegraph alarm signal is（）.

A.SOS sent three times
B.ten one-second dashes with a four-second interval between them
C.twelve four-second dashes with a one-second interval between them
D.twelve one-second dashes with a short interval between them