单项选择题
What is an ebb current（）.
A.A current at minimum flow B.A current coming in C.A current going out D.A current at maximum flow
单项选择题 What is a lighted safe water mark fitted with to aid in its identification（）.
单项选择题 What describes a flood current（）.
单项选择题 What area of the earth cannot be shown on a standard Mercator chart（）.
