The coach explained the regulations at length to make sure that none of his players would become violators.
【正确答案】 C
【答案解析】解析:译文为:教练详细地解释了规则以确保任何一个队员都不会违反。at length充分地,详尽地。at last最终;at once马上;in detail详细地;in short简言之。