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

单项选择题Under International Rules（）.

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

单项选择题The wind is ESE，and a sailing vessel is steering NW. Which fog signal should she sound?（）

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

单项选择题The term restricted visibility，when used in the Rules，refers to（）.

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

单项选择题The term power-driven vessel means（）in these Rules.

A.any sailing vessel with propelling machinery
B.any vessel propelled by machinery
C.any sailing vessel with or without machinery for propelling
D.any sailing vessel with propelling machinery not in use

单项选择题The steering and sailing rules for vessels in restricted visibility apply to vessels（）.

A.in sight of one another in fog
B.navigating in or near an area of restricted visibility
C.only if they are showing special purpose lights
D.only if they have operational radar