The correct order of steps taken by the United States to clean the air is:
- Establish funding to study how to clean the air.
- Create the EPA (Environmental Protection Agency).
- Enact the Clean Air Act.
- Find cost-effective ways to keep the air clean.
Therefore, the most accurate option among those provided is:
establish funding to study how to clean the air, create the EPA, enact the Clean Air Act, and find cost-effective ways to keep the air clean.
(Note: The specific enactment of the Clean Air Act happened in 1970, while the establishment of the EPA was also in the same year, but the need for funding and studies predates formal acts.)