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（）.
A.under existing visibility conditions B.under perfect visibility C.with ten miles visibility D.with fifteen miles visibility
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（）.
单项选择题 Restricted areas at locks and dams are indicated by（）.
