1.概念:表示过去某段时间或某一时刻正在发生或进行的行为或动作.
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 s+was/were+doing When he knocked at the door,his mother was cooking.
4.否定形式:s+was/were + not + doing.When he knocked at the door,his mother was not cooking.
5.一般疑问句:把was或were放于句首.(第一个字母大写)Was his mother cooking,when he knocked at the door?