4. 过去进行时
定义: 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去有上下文暗示外,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 + 动词-ing形式构成.
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