The boy was seen on the sports ground.A. to playB. playC. playedD. to playing

问题补充：

The boy was seen on the sports ground.

A. to play

B. play

C. played

D. to playing

答案：

(答案→)A. to play

B. play

C. played

D. to playing

解析：看某人做某事强调结果用see sb do sth，在被动句中用to do，本题为被动句，故用to play，故本题选A。