过去进行时

　　概念: 表示过去某一时刻或某一段时间正在进行的动作. 这一特定的过去时间除了有上下文暗示外,一般用时间状语来表示.

　　如: 1) ---What were you doing?

　　---I was jumping.

　　2) ---What was the boy doing when the UFO arrived?

　　---He was sleeping.

　　构成: 主语 + 助动词be(was/were) + 动词-ing形式构成.