The correct answer is: A. individuals in a species.
A population is a group of individuals of the same species that live in the same area at the same time. Populations can be very small, such as a group of bacteria in a puddle, or very large, such as the population of humans on Earth.
Species are groups of organisms that can interbreed and produce fertile offspring. Communities are groups of populations that interact with each other in an ecosystem. Ecosystems are systems that include all the living things in an area, as well as the non-living things that they interact with, such as the soil, water, and air.
Individuals in a family are not considered to be a population because they are not all the same species.