单项选择题
A.fixed red light B.Morse (A) white light C.composite group-flashing light D.yellow light
A light that has a light period shorter than its dark p...
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
A light having characteristics which include color vari...
单项选择题A light having characteristics which include color variations is defined as（）.
A.switching B.alternating C.oscillating D.fluctuating
A light characteristic of composite group flashing indi...
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
