单项选择题

A lighthouse can be identified by its（）.

A.painted color
B.light color and phase characteristic
C.type of structure
D.All of the above

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单项选择题
A lighted preferred-channel buoy may show a（）.

A.fixed red light
B.Morse (A) white light
C.composite group-flashing light
D.yellow light
单项选择题
A light that has a light period shorter than its dark period is described as（）.

A.flashing
B.pulsating
C.occulting
D.alternating
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