單項(xiàng)選擇題The period of a lighted aid to navigation refers to the（）.

A.date of construction or establishment
B.length of time between flashes of the light
C.time required for the longest flash of each cycle
D.time required for the light to complete each cycle


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1.單項(xiàng)選擇題The nominal range of a light may be accurately defined as the maximum distance at which a light may be seen（）.

A.under existing visibility conditions
B.under perfect visibility
C.with ten miles visibility
D.with fifteen miles visibility

2.單項(xiàng)選擇題The maximum distance at which a light may be seen under the existing visibility conditions is called（）.

A.nominal range
B.luminous range
C.charted range
D.geographic range

3.單項(xiàng)選擇題The luminous range of a light takes into account the（）.

A.glare from background lighting
B.existing visibility conditions
C.elevation of the light
D.observer's height of eye

4.單項(xiàng)選擇題Restricted areas at locks and dams are indicated by（）.

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

5.單項(xiàng)選擇題Preferred channel buoys indicate the preferred channel to transit by（）.

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