can be seen in the chart right here, the air pollution level in the city has been increasing over the last months.
A. What
B. It
C. that
D. As
网友回答
A. What
B. It
C. that
(答案→)D. As
解析： 考查as引导非限制性定语从句。题意 正如我们所看到的，空气污染水平在上月一直在增长。As代指 the air pollution level in the city has been increasing over the last months，故选 D项。
考点 非限制性定语从句。