Th answer would be D. a biome. A biome is distinguishable by its climate and what types of animals and plants live there. A community and a population are small classifications depending on specific species, so these are not correct. However, a biome could be easily confused with an ecosystem. Here is a quote form National Geographic to explain the difference “A biome is different from an ecosystem. An ecosystem is the interaction of living and nonliving things in an environment. A biome is a specific geographic area notable for the species living there. A biome can be made up of many ecosystems. For example, an aquatic biome can contain ecosystems such as coral reefs and kelp forests.”
Hope that helps :)