单项选择题
Underway vessels shall at all time maintain a proper look-out（）.
A.by sight and hearing only B.by all available means besides sight and hearing C.by all available means except sight and hearing D.by none of above means
单项选择题 Under International Rules（）.
单项选择题 The wind is ESE，and a sailing vessel is steering NW. Which fog signal should she sound?（）
单项选择题 The term restricted visibility，when used in the Rules，refers to（）.
