单项选择题
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
单项选择题 The radiotelegraph alarm signal is（）.
单项选择题 The expression FIRST MAGNITUDE is usually used to refer only to bodies of magnitude（）.
单项选择题 The expression DROP ANCHOR means（）.
