N a competitor who is at the back of a field in a race (赛跑中)落后者
call-back marker应答浮标;重返声控定位浮标
back marker buoy重返声控定位浮标
call-back marker buoy重返声控定位浮标
N(名词) a competitor who is at the back of a field in a race (赛跑中)落后者