单项选择题
Geographic range is the maximum distance at which a light may be seen under（）.
A.existing visibility conditions，limited only by the curvature of the Earth
B.perfect visibility conditions，limited only by the curvature of the Earth
C.existing visibility conditions，limited only by the intensity of the light
D.perfect visibility conditions，limited only by interference from background lighting
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单项选择题
Due to the shape of the sea anchor，the best way to haul it back aboard is by（）.
A.hauling in on the anchor line as you would any anchor
B.getting all hands to assist
C.its trip line
D.cutting the line，as you cannot haul it back in -
单项选择题
Deficient oxygen content inside a chain locker can be detected with（）.
A.litmus paper
B.a combustible gas indicator
C.an oxygen breathing apparatus
D.an oxygen indicator -
单项选择题
Continuous sounding of a fog whistle by a vessel is a signal（）.
A.that the vessel is anchored
B.to request the draw span of a bridge to be opened
C.of distress
D.that the vessel is broken down and drifting
