Final answer:
An ecosystem is a community of organisms and their physical environment, encompassing both living (biotic) and non-living (abiotic) components(option a).
Step-by-step explanation:
A community of organisms along with their physical environment constitutes an a)Ecosystem.
An ecosystem includes not only the biological community of trees, flowers, insects, and other living organisms but also the abiotic components such as water, soil, nitrogen, and sunlight. When we look at larger scopes, similar ecosystems with the same type of environment form a biome, and the biosphere is a collection of all ecosystems on Earth, encompassing all areas of life including land, water, and portions of the atmosphere.