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)（）.
单项选择题 A lateral system buoy displaying a quick light（）.
单项选择题 A great circle track provides the maximum saving in distance on（）.
