The correct answer is C. population
In biology,the term population signifies a group of individuals of the same species that live in the same place and are able to successfully reproduce among each other. Like in our example with the school of anchovies and a gaggle of geese.
A community is formed by multiple populations of the same species in an ecosystem. Therefore, 3 different gaggles of geese, or schools of anchovies would form a community of geese or anchovies.