Underway vessels shall at all time maintain a proper look-out（）.

A.all vessels must carry an after range light
B.vessels less than 50 meters in length need not carry an after range light
C.vessels stopped dead in the water should turn off their range lights
D.vessels over 20 meters in length must carry both range lights from sunset to sunrise

A.One blast at one-minute intervals
B.One blast at two-minute intervals
C.Two blasts at one-minute intervals
D.One prolonged and two short blasts at two-minute intervals

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