问题补充:
Now the air in our city is than it used to be. Something must be done to stop it.
A. good
B. bad
C. worse
D. better
答案:
A. good
B. bad
C. worse
D. better
解析: good形容词,好的;bad形容词,坏的;副词,很,非常,坏地;worse更坏的,更糟糕的;better更好的。联系下文,必须做点什么来组织这种情况。可知前文指的是,现在我们城市的空气比过去差多了。故选C。