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（）.
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)（）.
