单项选择题 Except for N-S courses，and E-W courses on the equator，a great circle track between two points，when compared to a rhumb line track between the same two points，will（）.

单项选择题 Buoys which only mark the left or right side of the channel will never exhibit a light with which characteristic? （）

单项选择题 Buoys which mark isolated dangers are painted with alternating（）.