单项选择题
The period of a lighted aid to navigation refers to the（）.
A.date of construction or establishment B.length of time between flashes of the light C.time required for the longest flash of each cycle D.time required for the light to complete each cycle
单项选择题 The nominal range of a light may be accurately defined as the maximum distance at which a light may be seen（）.
单项选择题 The maximum distance at which a light may be seen under the existing visibility conditions is called（）.
单项选择题 The luminous range of a light takes into account the（）.
