单项选择题
A.ignores the effect of surface currents B.is most useful when in sight of land C.must be plotted using magnetic courses D.may be started at an assumed position
A.north side of the mark B.west side of the mark C.east side of the mark D.south side of the mark
A.left-side buoy B.right-side buoy C.a buoy of safety D.a buoy of danger