The air quality in our city, is shown in the report, has improved a lot recently.
A. that
B. what
C. where
D. as
网友回答
A. that
B. what
C. where
(答案→)D. as
解析：句意：我们城市的空气质量，据报道已经改善了很多。这里是as引导的定语从句，as正如，在这里作主语，that不能引导非限制性定语从句；what不能引导定语从句，where在从句中不能作主语。故选D。