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單項(xiàng)選擇題

The positions and characteristics of lights and buoys shown within the port area are（）.

A.untrue
B.impossible
C.suspectful
D.unimportant

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