单项选择题
A.flashes at regular intervals at a frequency of 120 flashes or more per minute
B.is yellow in color
C.is visible over an arc of the horizon of not less than 180°nor more than 225°
D.All of the above
单项选择题 A drawbridge may use visual signals to acknowledge a vessel’s request to open the draw. Which signal indicates that the draw will NOT be opened immediately?（）.
单项选择题 A 95-meter vessel aground sounds which fog signal? （）
单项选择题 A 200-meter vessel restricted in her ability to maneuver，at anchor，will sound a fog signal of（）.