Final answer:
Oil and tire change service shops see increased profits as Americans keep older vehicles, which require more frequent maintenance such as oil changes and tire replacements.
Step-by-step explanation:
Oil and tire change service shops are experiencing a boom in profits primarily due to the c) Longer vehicle ownership leads to more maintenance needs.
Essentially, as Americans keep their vehicles for a longer time, regular maintenance like oil changes and tire replacements become more frequent to ensure the proper functioning and safety of the older vehicles.
Neither increased fuel efficiency, enhanced environmental regulations, nor decreased demand for oil changes is responsible for this profit increase in oil and tire service shops.
As vehicles age, they might also become less fuel efficient, necessitating more frequent service.
Furthermore, the provided options such as discovery of new oil or changes in the price of oil often relate to macroeconomic factors influencing oil production and pricing rather than the maintenance needs of vehicles directly.