Answer:
have fallen by more than one-half.
Explanation:
Thick, noticeable smog in many of the cities and manufacturing centers of the United States helped bring the 1970 e Clean Air Act to spur passage at the height of the national environmental movement. The ensuing modifications were intended to enhance its effectiveness and address newly recognized problems of air pollution such as acid rain and stratospheric ozone layer damage. The Clean Air Act allows EPA to set national environmental air quality levels for certain specific and prevalent contaminants, based on the latest research, to protect public health and welfare nationally. Certain main regulations are intended to reduce the rise in emissions from increasing motor vehicle numbers and new manufacturing plants.
The first amendment would be the answer.
