An endangered species is...

• A. A species with numbers so large that it dominates
• B. A species that migrates seasonally
• C. A species that is not yet discovered
• D. A species whose numbers are so small that extinction is a risk

Answer: (D)

The main idea being tested is how extinction risk relates to how many individuals of a species remain. An endangered status is assigned to species facing a high risk of extinction in the near future because their populations are very small or their habitats are severely threatened. When numbers are so low, random events, loss of genetic diversity, and ongoing threats can quickly push a species toward extinction, which is why this description fits best. The other statements describe unrelated traits—having a large population, seasonal migration, or not yet being discovered—that do not define the level of extinction risk.