单项选择题
A.glare from background lighting B.existing visibility conditions C.elevation of the light D.observer's height of eye
A.flashing red lights upstream and fixed red lights downstream B.yellow unlighted buoys C.signs and/or flashing red lights D.red daymarks upstream and green daymarks downstream
A.odd or even numbers B.the color of their top band C.the location of the buoy in the channel junction D.the buoy's light rhythms