Answer:
D. an ecosystem
Explanation:
An ecosystem is a community of living organisms (biotic factors) interacting with one another and their physical environment (abiotic factors). In an ecosystem, energy is transferred in a unidirectional manner from one organism to another when they feed on one another. For example, energy is transferred to a goat when it feeds on a plant.
Hence, this system in which energy transference occurs between the community of organisms is an ECOSYSTEM. The transfer of energy is one of the interactions between living organisms.
