單項(xiàng)選擇題

An alternating light（）.

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

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單項(xiàng)選擇題

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

單項(xiàng)選擇題

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

An alternating light（）.

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All persons or vessels within the lock area，including the lock approach channels，come under the authority of the（）.

A vessel which is being assisted by an icebreaker would display a flag hoist consisting of the code numeral 4 when the vessel（）.

All persons or vessels within the lock area，including the lock approach channels，come under the authority of the（）.