The answer is a. population will crash.
A carrying capacity is the maximum size of some population that can survive in the given environment. It represents the number of animals that can live, reproduce, survive in the given area regarding the indefinite sustainability of this area in terms of resources (food, water, habitat, etc.). If the animals reach the maximum number, thus, carrying capacity, the population will crash, which means that the number of animals will radically decrease due to diseases or predators.