单项选择题
What is a lighted safe water mark fitted with to aid in its identification（）.
A.A spherical topmark B.Red and white retroreflective material C.A sequential number D.A red and white octagon
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（）.
单项选择题 Traffic separation schemes adopted by the IMO are listed in（）.
