A) biome
Explanation - Biome is the ecological area where flora and fauna adapts themselves according to the environment or niche they are living in. An ecosystem is a group of living beings alongside the nonliving things of their condition, communicating as a framework.
Community is a group of organisms that interact with each other and carry out their work accordingly. Organism describes a particular being of a species. Therefore, Biome best suits the options given in the question.
Answer:
They are single celled organisms.
Explanation:
