单项选择题
A.the starboard side of the channel
B.the centerline of the channel
C.an obstruction where the preferred channel is to starboard
D.special purpose areas
单项选择题 During the day，a vessel with a tow over 200 meters in length will show（）.
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（）.