playground用on还是in
表示“在运动场上”或“在操场上”，playground前既可用介词in也可用介词on，但以用in为普通。例如：The children were all in[on]the playground。孩子们都在操场上。They are playing baseball in the playground。他们在运动场上打棒球。
用in的例证：children skipping in the playground在操场中跳绳的儿童；The children were out in the playground letting off steam。那些孩子在操场上玩，宣泄过剩的精力。
用on的例证：The children ran out and played on the playground at recess。休息的时候孩子奔出来到操场上玩耍。The boys chalked out goalposts on the playground wall。男孩子们在运动场的墙上用粉笔画上了球门柱。
另补充用at的例证：He supervised the children at the playground。他看管在操场上的孩子们。
