The correct option is D All above
An ecosystem consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows.
Fundamentally, ecosystem functions are exchange of energy and nutrients in the food chain. These exchanges sustain plant and animal life on the planet as well as the decomposition of organic matter and the production of biomass.
An ecosystem contains four functional aspects for its maintenance. These are biogeochemical cycles, energy flow, nutrient cycle, etc. Other important functional attributes are ecological succession, ecological pyramid, food web, and food chain.
Thus, the correct answer is "all the above".