Final answer:
The Clean Air Act has been a significant piece of environmental legislation with benefits greatly outweighing the costs and saving lives, despite its substantial implementation cost and political challenges. So, the correct answer is option e.
Step-by-step explanation:
The correct answer to the question about the Clean Air Act is E) All of the above are true. This act, since its inception, has had a tremendous financial and health impact on the United States. While implementation costs were significant, estimated at around $500 billion, the estimated health and other benefits have been remarkably higher, at an estimated $22 trillion.
Additionally, the act has indeed been challenged by Congress at various times, and also saved numerous lives, with an estimated 206,000 lives saved in 1990 alone. The Environmental Protection Agency (EPA) has also reported that benefits will continue to significantly exceed costs, further cementing the value of the Clean Air Act. So, the correct answer is option e.