Can you see the boys football on the playground? They are my classmates.A. to playB. play

问题补充：

Can you see the boys football on the playground? They are my classmates.

A. to play

B. playing

C. plays

D. Played

答案：

A. to play

(答案→)B. playing

C. plays

D. Played

解析：句意：你能看到操场上正在踢足球的男孩子吗？他们是我的同班同学。see sb. doing看到某人正在做某事，故选B。