现在完成时

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：yet,already,just,never,ever,so far,by now,since+时间点，for+时间段，recently, lately, in the past few years, etc.

3.基本结构：主语+have/has +p.p（过去分词）+其他

4.否定形式：主语+have/has + not +p.p（过去分词）+其他

5.一般疑问句：have或has。

6.例句：I've written an article.

           The countryside has changed a lot in the past few years.