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?