單項選擇題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


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1.單項選擇題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

2.單項選擇題The expression DROP ANCHOR means（）.

A.hold anchor
B.leave anchor
C.let go anchor
D.weigh anchor

3.單項選擇題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

5.單項選擇題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