单项选择题
A.Safe water mark
B.Isolated danger mark
C.Preferred channel mark
D.Daymark of no lateral significance
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（）.
单项选择题 When latitude and longitude are used，these shall be expressed in（）（and decimals of a minute if necessary），north or south of the Equator and east or west of Greenwich.