过去进行时 — 英语填空题
题目
Yesterday evening, while the police ___ (search) the park for the lost schoolbag, a witness told them that at 8 o'clock last night, he ___ (see) a tall man ___ (walk) quickly out of the park with a bag in his hand. According to the clues, the man was the suspect.（用所给动词的适当形式填空）