At no time in history has there been such a mass migration of peo_英语解答

At no time in history has there been such a mass migration of people from countryside to city as is happening now.
句中“as”有何用法?

人气：158 ℃　时间：2020-02-04 21:05:00

解答

此处"as"的意思是正如.
e.g.as is known to all 众所周知正如现在发生的？