Final answer:
Longer life spans in the United States are attributed to a combination of factors including decreased air pollution, improved health care, and improved diet, all of which have resulted in a collective impact on longevity.
Step-by-step explanation:
The factors that have contributed to longer life spans in the United States include decreased air pollution, improved health care, and improved diet. Regarding air pollution, the new regulations and advancements in technology have decreased the levels of harmful pollutants, reducing health risks related to respiratory and cardiovascular diseases. In the context of healthcare, the development and spread of vaccinations, antibiotics, and advancements in medical technology and procedures have drastically reduced mortality rates. Improved dietary choices and awareness of nutrition have also played a significant role, as has the reduction in behaviors such as smoking and increased emphasis on regular exercise. Hence, all of the listed responses have collectively contributed to the rise in life expectancy.