The natural resources used by society are limited by various factors. Why is coal considered a nonrenewable resource? a. Once coal is used up, it can never be replaced. b. Coal is a nonrenewable resource, because it comes from the impact of meteors with the Earth. c. Coal was a renewable resource, until it was mismanaged by humans. d. Coal is considered a nonrenewable resource, because it takes millions of years to form. Please select the best answer from the choices provided