单项选择题
A white buoy with an orange rectangle on it displays（）.
A.directions B.dangers C.exclusion areas D.All of the above
单项选择题 A white buoy with an open-faced orange diamond on it indicates（）.
单项选择题 A white buoy with a blue band is（）.
单项选择题 A V-shaped ripple with the point of the V pointing upstream in a river may indicate a（）.
