----Where is Jack?--On the playground. He football with his classmates. A. playB. play

问题补充：

----Where is Jack?

----On the playground. He football with his classmates.

A. play

B. played

C. is playing

D. was playing

答案：

A. play

B. played

(答案→)C. is playing

D. was playing

解析：句意：杰克在哪儿？——在操场上，他正在操场上和他的同学们踢足球。结合语境可知本句中描述的是现在正在进行的动作，故选C。