In stopping distances of vessels，head reach can best be described as the（）.

A.difference between the vessel's speed through the water at any instant and the new speed ordered on the telegraph
B.distance the vessel has actually run through the water since a change of speed was ordered
C.distance the vessel will run between taking action to stop her and being stationary in the water
D.speed at which a vessel should proceed to ensure that she will run a predetermined distance，once her engines have been stopped