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（）.
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（）.
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（）.
