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.

The answer is D. Coal is considered as a nonrenewable resource because it takes million of years to form. Coal is formed by the alteration of peat chemically and physically. The process of coal formation is called coalification. During  this  process, peat experiences a lot of processes like heat, a lot of pressure and bacterial decay where oxygen is forced out and what's left is carbon deposits which in due time forms coal.