过去进行时的结构及句型变化
过去进行时由"was / were + 现在分词"构成。如：
I was doing my lessons then. 那时，我在做功课。
We were cleaning the house. 我们在打扫房子。
过去将来时态的肯定句、否定句和疑问句形式：
肯定句例句：I was walking down the street when a UFO landed.
否定句例句：I wasn’t walking down the street when a UFO landed.
一般疑问句例句：Were you walking down the street when a UFO landed?
特殊疑问句例句：What were you doing when a UFO landed?