单项选择题
A dead reckoning (DR) plot（）.
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
单项选择题 A cardinal mark showing an uninterrupted quick-flashing white light indicates the deepest water in the area is on the（）.
单项选择题 A buoy，being a shape of cylinder and with red group flashing，shows that it is（）.
单项选择题 A buoy with a composite group-flashing light indicates a(n)（）.
