单项选择题
A.2 to 4 seconds
B.4 to 6 seconds
C.6 to 8 seconds
D.8 to 10 seconds
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?()
单项选择题 On entering from seaward,a starboard side daymark will().
单项选择题 Navigation lights must be displayed in all weathers from sunset to sunrise. They also().