The correct answer is option C. the variety of the organisms.
The population size can be defined as the actual number of the individuals present in an organism. The presence of the variety of the organism does not effect the population size as they do not have any effect on the reproduction.
Reason for the incorrect answers:
The total number of the organism has a direct impact on the population size of the organism. In case, the total number of the organism is high, the population size would increase at a higher rate, and if the total number of individual are less than the population would not increase at a higher rate.
The available water supply and adequate shelter would also effect the size of the population. In case, the adequate shelter and the water supply would be available, then in the presence of the abundant resources, the organism would reproduce at a higher rate and the population size would increase, and the opposite occur in lack of resources, in the absence of adequate resource, the organism reproduce at a slower rate and mortality can be high.
