2.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。

3.基本结构 主语+was/were +doing +其它

4.否定形式：主语+was/were + not +doing+其它

5.一般疑问句：把was或were放于句首。(第一个字母大写)

6.例句：At that time she was working in a PLA unit.那段时间她在人民解放军部队工作。

When he came in,I was reading a newspaper.他进来时，我正在读报纸。