1.正确答案：C.
2.该题最好能把它还原成陈述句来理
This is the way you think of ____ the city of white pollution in practice.
3.所以,该题主干是This is the way.
其后是一个定语从句,修饰先行词the way.
根据定语从句的语法,把先行词the way放入后面的句子中去,即：
you think of the way ____ the city of white pollution in practice.
因为关系代词which/that代替先行词the way在上述定语从句中做think of的宾语,所以关系代词which/that可以省略不写.
4.该定语从句中,the way做think of的宾语,而____ the city of white pollution in practice又是the way的后置定语.
不知道楼主听说过这两个固定搭配没有：
the way to do sth = the way of doing sth “做某事的方法”
所以,该题的答案应该是：to rid 或 of ridding.