A yellow signal，floating in the air from a parachute，about 300 feet above the water，indicates that a submarine（）.

单项选择题A vessel，which does not normally engage in towing operations，is towing a vessel in distress.She（）.

A.need not show the lights for a vessel engaged in towing，if it is impractical to do so
B.may show the lights for a vessel not under command
C.must show a yellow light above the stern light
D.must show the lights for a vessel towing

单项选择题A vessel sounding a fog signal of one short，one prolonged，and one short blast is indicating that the vessel is（）.

A.fishing
B.in distress
C.at anchor
D.not under command

单项选择题A vessel showing a yellow light over a white light at night is a vessel（）.

A.engaged in piloting
B.towing astern
C.engaged in fishing
D.in distress

单项选择题A vessel shall，so far as practicable，（）traffic lanes.

A.avoid cross
B.avoid to cross
C.avoid crossly
D.avoid crossing

单项选择题A vessel is approaching from dead ahead.Both of her sidelights are visible and her range lights are in line.Which of the following could you do first（）.

A.Sound one blast of the whistle
B.Alter course to starboard
C.Construct a radar plot
D.Sound the danger signal