时间状语：at this time yesterday, at that time或以when引导的谓语动词是一般过去时的时间状语等。
基本结构：was/were + doing
否定形式：was/were + not + doing.
例句：At that time she was working in a PLA unit.
When he came in, I was reading a newspaper. II.过去完成时
时间状语：before, by the end of last year(term, month…),etc.
基本结构：had + done.
否定形式：had + not + done.
例句：As soon as we got to the station, the train had left.
By the end of last month, we had reviewed four books III.过去将来时
时间状语：the next day(morning, year…),the following month(week…),etc.
基本结构：was/were/going to + do；would/should + do.
否定形式：was/were/not + going to + do; would/should + not + do.
例句：He said he would go to Beijing the next day.
I asked who was going there.