Large vessel leaving. Keep clear（）approach channel.

A.implemented
B.implied
C.impossible
D.improper

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

A.one short blast
B.one prolonged blast
C.not less than five short blasts
D.not less than five prolonged blasts