USCG Navigation General Questions: Master's License. 1: Unlighted, red and green, horizontally-banded buoys with the topmost band red ____________. A: are cylindrical in shape and called can buoys. B: are conical in shape and called nun buoys. C: may either be cylindrical or conical since the shape has no significance. D: are triangular in shape to indicate that it may not be. 2: On an isomagnetic chart, the line of zero variation is the __________. A: zero variation line.