Refer to the graph. A graph titled Total Deaths from Air Pollution by Region, 1990 and 2013 shows regions on the x axis and number of deaths on the y axis. The graph shows a downward trend from years 1990 to 2013 for Europe, Central Asia, and North America.

Which of the following best explains the change in number of deaths from air pollution in Europe and Central Asia and in North America from 1990 to 2013?

Reduced consumption of manufactured goods
Greater reliance on coal and natural gas for power
Falling birth rates resulting in smaller populations and less pollution
Increased government regulation of manufacturing and transportation