单项选择题
The duration of a prolonged blast of the whistle is（）.
A.2 to 4 seconds
B.4 to 6 seconds
C.6 to 8 seconds
D.8 to 10 seconds
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相关考题
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单项选择题
Some lights used as aids to marine navigation have a red sector to indicate a danger area. The limits of a colored sector of a light are listed in the Light List in which of the following manners?（）
A.Geographical positions outlining the area of the sector
B.True bearings as observed from the ship toward the light
C.An outline of the area of the sector
D.True bearings as observed from the light toward the ship -
单项选择题
On entering from seaward，a starboard side daymark will（）.
A.show a fixed red light if lighted
B.show a Morse (A) white light
C.be square in shape
D.have an even number if numbered -
单项选择题
Navigation lights must be displayed in all weathers from sunset to sunrise. They also（）.
A.must be displayed when day signals are being used
B.must be displayed when moored to a pier
C.may be extinguished at night on open waters when no other vessels are in the area
D.may be displayed during daylight
