同学你好，该知识点来自沪江网校《韩语入门至生活会话流畅丨试学班》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
时间作主语+has/have+ witnessed, seen, experienced+其他，比如
The past few years have witnessed dramatic increase in the difficulty of examinations and employment.
过去几年中，考试和就业的难度都在剧烈增加。
The past five years have seen major progress.
在过去五年中取得了重大进展。


has been happening是现在完成进行时。
现在完成进行时 have been doing 强调的是持续性的过程，而现在完成时 have done 则侧重于这个动作所造成的结果和影响。
I have read the book. 我读过这本书。
I have been reading the book. 我一直在读这本书。  

这里something has been happening强调这个动作一直在持续，一直在发生

祝同学学习进步~