单项选择题
A yellow buoy may mark a(n)（）.
A.wreck B.shoal area C.anchorage area D.middle ground
单项选择题 A yellow buoy may exhibit a(n)（）.
单项选择题 A white buoy with an orange rectangle on it displays（）.
单项选择题 A white buoy with an open-faced orange diamond on it indicates（）.
