单项选择题
Which of the following are data layer categories to be displayed on ECDIS（）．
A.ECDIS warnings and messages B.Hydrographic Office data C.Notice to Mariners information D.All of the above
单项选择题 Which buoy will NOT display white retro reflective material（）.
单项选择题 When using horizontal sextant angles of three objects to fix your position，an indeterminate position will result in which situation（）.
单项选择题 When navigating a vessel，you（）.
