The correct option is C, that is, A SEASON OF EXTRA RAIN.
The carrying capacity for a population within an ecosystem gives us information about the number of that particular specie that the ecosystem can support. There are many factors that can increase or decreases the carrying capacity of an ecosystem.
In the scenario given in the question, a season of extra rain will increase the carrying capacity of the population, this is because, a season of extra rain will bring about extra bountiful growth of grasses, which will serve as food to the population, thus, there will be an increase in the quantity of food resources that are available, this is in turn will increase the carrying capacity of the population.