Buoys which mark dredging areas are painted（）.

A.A safe-water buoy will display red and white vertical stripes of reflective material
B.All reflective material is white because it is the most visible at night
C.A special-purpose mark will display either red or green reflective material to agree with its shape
D.A preferred-channel buoy displays either red or green reflective material to agree with the top band of color

A.a hard sand shoal marked with a light
B.completely submerged at all stages of the tide
C.surrounded by rocks awash at low water spring tides
D.a small，low，sandy islet surrounded by shoal water

A.directions
B.distances
C.locations
D.All of the above