Good anchorage may be obtained anywhere in this water area，the bottom being generally mud and sand，vessel may have（）.

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

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

单项选择题Before entering the chain locker，you should（）.

A.have someone standing by
B.make sure there is sufficient air within the locker
C.de-energize the windlass
D.All of the above