Which statement best describes why a pond ecosystem could be considered an open system? a. the energy from sunlight enters the system creating new energy; all matter is contained within the food chain. b. energy is contained within the pond ecosystem and is transferred within the system. c. as sunlight, predators, and prey enter or exit the system, energy and matter move freely into and out of the system. d. no energy exists beyond the pond ecosystem so it does not have any effect on the system.