单项选择题
With the help of modern technology, ships are able to receive automated broadcast of safety messages（）.
A.by day or at night B.almost round the clock C.somewhat and sometime D.from sunrise and sunset
单项选择题 A radio determination system based on the comparison of reference signals with radio signals reflected,or retransmitted from the position to be determined,is（）.
单项选择题 What information will a distress alert contain?（）
单项选择题 The ARQ mode should be applied（）.
