单项选择题 Daymarks marking the starboard side of the channel when going towards the sea are（）.

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?（）.