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
单项选择题The expression FIRST MAGNITUDE is usually used to refer only to bodies of magnitude（）.
A.1.5 and greater B.1.25 and greater C.1.0 and greater D.0.5 and greater
单项选择题The expression DROP ANCHOR means（）.
A.hold anchor B.leave anchor C.let go anchor D.weigh anchor
单项选择题The best method to stop a vessel from dragging anchor in a sand bottom is to（）.
A.reduce the length of the cable B.pay out more anchor cable C.back the engines D.swing the rudder several times to work the anchor into the bottom
单项选择题PAN-PAN repeated three times over the radiotelephone indicates which type of message will follow?（）
A.Distress B.Safety C.All clear D.Urgency
单项选择题In radiotelephone communications，the prefix PAN-PAN indicates that（）.
A.a ship is threatened by grave and imminent danger and requests immediate assistance B.a calling station has an urgent message about the safety of a person C.the message following the prefix will be about the safety of navigation D.the message following is a meteorological warning
