互动封闭仿真课堂
1、智能交互 2、电子板书式视频教学 3、在线互动问答 4、封闭课堂启发式教学方式
随堂测试、知识梳理、易错点揭示、总结启迪智能错题本
听课中的错题能自动加入错题本，课后可方便复习及导出错题本升级服务
在线答疑、课后同类题练习、讲义下载、短信提醒I didn't know you were so busy.
3.基本结构：was/were doing
4.否定形式：was/were not doing.
5.一般疑问句：把was或were放于句首。
6.例句：At that time she was working in a PLA unit.
When he came in, I was reading a newspaper.
1.概念：过去发生或已经完成的动作对现在造成的影响或结果，或从过去已经开始，持续到现在的动作或状态。
2.时间状语：recently, lately, since…for…,in the past few years, etc.
3.基本结构：have/has done
4.否定形式：have/has not d one.
5.一般疑问句：have或has。
6.例句：I've written an article.
It has been raining these days.
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