Final answer:
Fossil fuels are considered nonrenewable energy sources because they cannot be easily replaced as fast as they are consumed and take millions of years to form.
Step-by-step explanation:
The nonrenewable energy source among the options given is fossil fuels. Fossil fuels, such as oil, natural gas, and coal, cannot be easily replaced as fast as they are consumed and take millions of years to form. About 85% of our energy comes from nonrenewable fossil fuels.