A population of wild boar has grown in size. Officials meet to identify different ways to stop this growth. They reduce food supply for the wild boar and modify the environment, causing the wild boar to stop reproduction. After making these changes, they notice that the population has stabilized. Which is the dependent variable in this experiment?

a. the population size of wild boar in the environment
b. the type of method used to stop wild boar growth
c. the environment in which the wild boar lives
d. the time it takes for the wild boar population to grow