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、短信提醒五、but的用法:
but用作关系代词, 其意思相当于who/that…not…, "没有……不……", 如：
1.There is not one of us but wishes to help you.
2.There is no tree but bears some fruit.
3.There are very few but admire his talents.
Ⅲ. 关系副词引导的定语从句:
When 指时间，在定语从句中作时间状语。其先行词是表时间的名词(如：time, day, week, tear, month, etc.)
1. He came last night when I was out.
2. We will put off the picnic until next week, when the weather would be better.
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