Answer:
The correct answers would be natural selection and high genetic variation in the species.
Natural selection refers to the natural phenomenon by which organisms which are better adapted or have survival traits tend to survive and reproduce more in the environment.
It leads to an increase in the frequency of the trait in a population.
Genetic variation refers to the sum total of all the genetic characteristics present in a population. Higher genetic diversity higher are the chances of a population to survive.
Similarly, different sizes of the beaks are the result of high genetic diversity out of which large size beak was favored by natural selection.
Ultimately, the large beak size trait spreads through the population.
