​All of the Following Statements Are True About Air Pollution

​All of the following statements are true about air pollution except that:

A) it contributes to a higher incidence of pneumonia, emphysema, lung cancer, and bronchitis.
B) ​it is most severe in large, densely populated industrial centers.
C) ​plains and mountains are more likely to have air pollution than valleys and closed air basins.
D) ​poor visibility caused by smog is recognized as a major factor in both airplane and automobile accidents.