the headmasteu saw the children playing on the playground (变成复合句）the headmasteu saw the children ()()on the playground
网友回答
The headmaster saw the children (are) (playing) on the playground.
======以下答案可供参考======
供参考答案1:
1.were playing(宾语从句）省略了the children前的that
2.were playing(定语从句）省略了the children后面的that或是who
两句答案虽一样，但翻译是不一样的
1.校长看到了那些孩子在操场上玩
2.校长看到了那些在操场上玩的孩子
这是概念问题，但是答案were playing肯定是对的，无论是定语从句还是宾语从句，根据题意都应该用过去进行时