过去进行时由 was/were 加现在分词构成。
例如：
What were you doing this time yesterday?昨天这个时候你在做什么?
During the summer of 1999 she was travelling in Europe.1999年夏天她在欧洲旅行。
He said he was leaving for home in a day or two. 他说他一两天之内就动身回家了。
She was always thinking of others. 她老是想到别人。(赞扬)
She was forever complaining. 她老是抱怨。(厌烦)
I was reading the newspaper when the doorbell rang. 我正在看报，突然门铃响了。
Jim burnt his hand when he was cooking the dinner. 吉姆做饭时把手烫了。
I met Diana while I was shopping this morning. 我今早买东西时碰到了戴安娜。
I was doing my homework while he was listening to music. 我在做作业而他在听音乐。