单项选择题
A.bottom contour only up to depths of 100 fathoms B.depth underneath the keel against a time base C.contour of the bottom against a distance base D.depth of water against a distance base
The points on the earth’s surface where the magnetic di...
单项选择题The points on the earth’s surface where the magnetic dip is 90° are（）.
A.Along the magnetic equator B.Connected by the isoclinal line C.The isopors D.The magnetic poles
The four standard light colors used for lighted aids to...
单项选择题The four standard light colors used for lighted aids to navigation are red，green，white，and （）.
A.purple B.orange C.blue D.yellow
The equator is（）.A.the primary great circle of the Eart...
单项选择题The equator is（）.
A.the primary great circle of the Earth perpendicular to the axis B.the line to which all celestial observations are reduced C.the line from which a celestial body's altitude is measured D.All of the above
