Which of four factors that affect evolution apply to the finches that the Grants studied?

The Grants have focused their research on the medium ground finch, Geospiza fortis, on the small island of Daphne Major. Daphne Major serves as an ideal site for research because the finches have few predators or competitors. (The only other finch on the island is the cactus finch.) The major factor influencing survival of the medium ground finch is the weather, and thus the availability of food. The medium ground finch has a stubby beak and eats mostly seeds. Medium ground finches are variable in size and shape, which makes them a good subject for a study of evolution.

Explanation:

the correct option is option a

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.