The two vessels underway may collide with（），if they don’t take immediate measures.

A.Situations when you can see vessels on radar that you cannot see visually
B.Visibility of less than half a mile
C.Any condition where visibility is restricted
D.Visibility where you cannot see shore

A.a blast of from five to seven seconds' duration
B.a blast of from five to six seconds' duration
C.a blast of from four to six seconds' duration
D.a blast of from six to seven seconds' duration

A.Whenever two vessels approach from opposite directions
B.If the bearing of an approaching vessel does not appreciably change
C.Whenever a vessel crosses ahead of the intended track of another vessel
D.If one vessel approaches another so as to be overtaking