单选题
The footballer has been bouncing the ball for hours {{U}}on end{{/U}}, and appears capable of more hours.
【正确答案】
C
【答案解析】[分析] 固定搭配
on end表：竖着，连续地；A．now and then偶尔；B．untiringly不疲倦地，不屈不挠地； C．without interruption不间断地，继续不断地；D．breathlessly气喘地，屏息地，闷热地；所以答案为C。