单项选择题
A.shows a light with varying lengths of the lighted period B.shows a light that changes color C.marks an alternate lesser-used channel D.is used as a replacement for another light
All persons or vessels within the lock area，including t...
单项选择题All persons or vessels within the lock area，including the lock approach channels，come under the authority of the（）.
A.dockmaster B.dock captain C.lockmaster D.lock foreman
A vessel which is being assisted by an icebreaker would...
单项选择题A vessel which is being assisted by an icebreaker would display a flag hoist consisting of the code numeral 4 when the vessel（）.
A.speed begins to drop B.stops C.receives ice damage D.becomes icebound
A vessel which is being assisted by an icebreaker shoul...
单项选择题A vessel which is being assisted by an icebreaker should indicate that she is ready to cast off the towline by（）.
A.displaying code letter Y (Yankee) B.sounding five short blasts on his whistle C.displaying code numeral 5 D.sounding one prolonged blast on his whistle
