The air quality in the city, ______ is shown in the report, has improved over the past two months.
问题描述：
The air quality in the city, ______ is shown in the report, has improved over the past two months.
A. that B. it C. asD. what
四个选项如何区分
答
C
这是as 引导的非限制性定语从句,as 代替整个主句,B,D 不是关系词,而that 不可引导非限制性定语从句