单项选择题
A.with part of it extending above the water
B.that can be detected by water turbulence
C.that drops off sharply
D.perpendicular to the current
单项选择题 （）means the curve on the earth’s surface which cuts all the meridians at the same angle.
单项选择题 （）is the process by which the position of the vessel at any moment is found by applying the last well-determined position to the run that has been made since，using for this purpose the ship’s course and the distance being those indicated by log.
单项选择题 Leeway is the（）.