单项选择题
A.from sunset to sunrise and during restricted visibility
B.only when other vessels are in the area
C.only when operating in a traffic separation scheme
D.only when under tow
单项选择题 The International Regulations for Preventing Collisions at Sea contain the requirements for （）.
单项选择题 The duration of a prolonged blast of the whistle is（）.
单项选择题 Some lights used as aids to marine navigation have a red sector to indicate a danger area. The limits of a colored sector of a light are listed in the Light List in which of the following manners?（）