单项选择题
A white buoy with an open-faced orange diamond on it indicates（）.
A.danger B.vessels are excluded from the area C.the buoy is a mooring buoy D.operating restrictions are in effect
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（）.
单项选择题 A vessel is（）when she is not at anchor，made fast to the shore，or aground.
