Now the air in our city is than it used to beSomething must be done to stop it．A. very g

问题补充：

Now the air in our city is than it used to be．Something must be done to stop it．

A. very good

B. much better

C. rather bad

D. even worse

答案：

A. very good

B. much better

C. rather bad

(答案→)D. even worse

解析：结合下文，必须做些事来阻止这种情况。可知上文句意为：现在我们市的空气比过去差多了。Than前面一般用比较级形式，结合语境可知选D。