What is the population size or density of a species affected by?
Only birth rate
Only death rate
Both birth rate and death rate
Sex ratio
Correct option (C) Both birth rate and death rate
The population size or density of a species is affected by both birth rate (natality) and death rate (mortality). Birth rate is the rate at which new individuals are produced in the population, whereas death rate is the rate at which individuals are lost from the population due to various factors. Therefore, both birth rate and death rate have an impact on the population size or density. Sex ratio, on the other hand, refers to the proportion of males and females in the population and does not directly affect the population size or density.
Option c is the correct answer.