Final answer:
The correct answer is option C, a community. A community includes all populations of different species that reside in the same area and interact with each other, thus comprising the biotic factors of that area.
Step-by-step explanation:
A group of interacting species that occur together at the same place and time is known as a community. This is option C in the given list. By definition, a population refers to a group of organisms of the same species that live in the same area and interact with one another. Meanwhile, a community encompasses all of the populations of different species that live in the same area and interact with each other, composing all the biotic factors of that area. Therefore, populations of a single species form constituents of a community, and ecological studies at the community level help to understand the interactions and competition for resources among different species within the same habitat.