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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单项选择题

A light having characteristics which include color variations is defined as（）.

A.switching
B.alternating
C.oscillating
D.fluctuating

单项选择题

A light characteristic of composite group flashing indicates that there is a(n)（）.

A.sharp turn in the channel
B.narrowing in the channel at that point
C.junction in the channel
D.obstruction that must be left to port

单项选择题

A lateral system buoy displaying a quick light（）.

A.should be passed close aboard on either side
B.indicates that special caution is required
C.is used at a channel bifurcation or junction
D.is painted with red and white vertical stripes