Q.Which of the following is / are not a natural ecosystem?

An ecosystem is the basic functional unit of ecology, built from two interacting classes of component. The abiotic (non-living) class covers climatic factors (air, water, sunlight, rainfall, temperature, humidity), edaphic factors tied to soil, topographic factors (latitude, altitude), and the organic/inorganic substances present — their total pool at a given time is called the ecosystem's standing quality or standing state. The biotic (living) class covers every organism present, split functionally into autotrophic producers (chiefly green plants, which manufacture organic compounds from inorganic raw material via photosynthesis) and heterotrophic consumers/decomposers (macroconsumers — herbivores, carnivores, omnivores — and microconsumers, i.e. decomposers such as bacteria, actinomycetes and fungi, which break down dead matter and release its nutrients for reuse). The amount of living material present in a population at a given time is its standing crop, measured either in numbers or as biomass (fresh, dry, or carbon weight) per unit area. Functionally, an ecosystem performs three linked jobs: creating usable energy (via producers capturing sunlight), transferring that energy from organism to organism, and cycling nutrients between the living community and its non-living surroundings. Every ecosystem, regardless of type, ultimately runs on this same structure-plus-function template, and every other topic in ecology — food chains, pyramids, decomposition, nutrient cycling, ecosystem services — is really just a different lens on how this basic structure functions in practice.