单项选择题
A buoy，being a shape of cylinder and with red group flashing，shows that it is（）.
A.left-side buoy B.right-side buoy C.a buoy of safety D.a buoy of danger
单项选择题 A buoy with a composite group-flashing light indicates a(n)（）.
单项选择题 A buoy marking a wreck will show a(n)（）.
单项选择题 A buoy having red and green horizontal bands would have a light characteristic of（）.
