A V-shaped ripple with the point of the V pointing upstream in a river may indicate a _____.
A.submerged rock, not dangerous to navigation
B.broken wreck, not dangerous to navigation
C.towed-under buoy
D.All of the above
正确答案：C
尖头向上游的V形小浪表明其下有碍航物
AV-shapedripplewiththepointoftheVpointingupstream
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