The Reduction of Outdoor Air Pollution in the United States

The reduction of outdoor air pollution in the United States has been so successful because:

A) The U.S. Congress supported it and diligently crafted laws to ensure its success.
B) U.S. citizens insisted that the laws be passed.
C) The country is affluent enough to afford the controls and improvements it required.
D) All of these answers are correct.
E) Only U.S. citizens insisted that the laws be passed and the country is affluent enough to afford the controls and improvements it required are correct.