—Where were you at ten o’clock this morning?—I with my friends in the park at that time.A

问题补充：

—Where were you at ten o’clock this morning?

—I with my friends in the park at that time.

A. fly kites

B. am flying kites

C. was flying kites

D. flew kites

答案：

A. fly kites

B. am flying kites

(答案→)C. was flying kites

D. flew kites

解析：句意：今天上午十点你在哪儿？——那时我正在公园和我的朋友们放风筝。结合语境可知下文描述的是过去某时正在进行的动作，故用过去进行时态，选C。