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
单项选择题 A light having characteristics which include color variations is defined as（）.
单项选择题 A light characteristic of composite group flashing indicates that there is a(n)（）.
单项选择题 A lateral system buoy displaying a quick light（）.
