游戏规则的表达 — 英语选择题

玩套圈游戏时，选手必须站在线后投圈，投圈时不能踩线。哪句话正确表达了这两条规则？A. You can stand on the line and throw. B. You must stand behind the line, and you can't step on it when you throw. C. You must stand behind the line, but you can step on it when you throw. D. You can stand in front of the line, but you can't throw.