A.Three shapes，the highest and lowest shall be red ball……

单项选择题Dring a period of “whiteout”，you should expect which of the following（）.

A.Snowfall or blowing snow
B.Lack of ability to estimate distance
C.Harsh contrast between sun-illuminated snow cover and the background
D.Hazy horizons with extensive mirage effects

单项选择题Day-shapes must be displayed（）.

A.Between sunset and sunrise
B.Only between 8 AM and 4 PM
C.During daylight hours in any visibility
D.During daylight hours in unrestricted visibility only

单项选择题At night，a vessel shall indicate that she is restricted in her ability to maneuver by showing in a vertical line two（）.

A.red lights
B.red lights and two white lights
C.red lights with a white light in between
D.white lights with a red light in between

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

A.will be coming to periscope depth
B.will be coming to the surface
C.is on the bottom in distress
D.is in distress and will try to surface

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