Thanks for all the explanation but could anyone please explain why we can get the inference on D from the passage as well? I can now understand why C is wrong but still could not get my head around on D besides eliminating the other four.

Great discussion! The thing that really bothers me about answer "C" is the prase "anywhere else," could the anywhere else include the places where there is a large amount of other pollulants and a small amount of soot? If that's the case, doesn't it somehow weaken the argument? a...