A fairly accurate estimation of a ship’s position can be calculated by a technique known as（）.

A.must utilize magnetic courses
B.must take set and drift into account
C.should be replotted hourly
D.should be started each time the vessel's position is fixed

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