The old man was seen in the park at 7:00 a.m. yesterday.A. exercise B. exercisedC. to exe

问题补充：

The old man was seen in the park at 7:00 a.m. yesterday.

A. exercise

B. exercised

C. to exercise

D. exercising

答案：

A. exercise

B. exercised

C. to exercise

(答案→)D. exercising

解析：see sb doing sth表示看到某人正在做某事。