The correct answer is D. An unmanaged resource that is limitless.
Step-by-step explanation
Sustainable resources are those natural resources that can be used today without compromising the resources and possibilities of future generations. Sustainable resources are characterized for being limitless and not being produced by humans, that is, generated by nature, for example, solar energy, wind energy, hydraulic energy (from water), among others. Unlike non-renewable resources are those that have a limit, such as water, oil, natural gas, among others. Therefore, the correct answer is D. An unmanaged resource that is limitless.