单项选择题 By night，you sight the lights of a vessel engaged in underwater operations. If an obstruction exists on the port side of the vessel，it will be marked by（）.

单项选择题 At sea，you are approaching a small vessel and see that it has the signal flag P hoisted. What should you do?（）.

单项选择题 As defined in the Rules，a towing light is a yellow light having the same characteristics as a(n)（）.