表示在“在操场上”，playground前面通常用介词in，有时也用介词on。如：

The children wereskipping in the playground (on the playground). 孩子们在操场上跳绳。

Sam pushed meover in the playground (on the playground). 萨姆在运动场上把我推倒了。

Therewere children fighting in the playground (on theplayground). 有小孩在操场上打架。

The childrenwere running about in the playground (on the playground). 孩子们在运动场上跑来跑去。

人教版英语教材必修一第11页认为：用in为英国英语，用on为美国英语。