Concept:In an ecosystem, matter is recycled continuously, but energy is not recycled.
Explanation:Sweat, urea, and carbon dioxide are forms of matter lost from a mammal's body.
These substances can enter biogeochemical cycles and be reused by the ecosystem.
Heat energy, however, is dissipated into the surroundings as thermal energy.
This heat cannot be recaptured or cycled back into the ecosystem.
Therefore, heat energy is the substance that will not be returned to the ecosystem.
Answer:C. Heat energy