Question

how did the amount of snowfall affect the feather density of parus major through natural selection?
the number of birds with different feather densities stayed the same. this suggests additional snowfall had no effect on feather density.
more birds had higher feather density when there was more snowfall. this suggests birds with denser feathers were better at surviving colder conditions.
more birds had lower feather density when there was more snowfall. this suggests birds with fewer feathers were better at surviving colder conditions.
more birds first had lower feather density; then their density increased as snowfall increased. this suggests feather density changed randomly.

Explanation:

Natural selection favors traits that enhance survival. In colder (more snowfall) conditions, birds with denser feathers (higher feather density) would be better insulated. Looking at the table: as the snowfall - related range (assuming the left - hand column is related to snowfall in some way, and the right - hand column is the number of birds), when the "snowfall - related" range increases (from 40.0 - 44.9 to 57.0 - 60.9), the number of birds in the higher feather - density group (assuming the right - hand side of the table columns represents higher feather density as the values on the right increase from 3 to 17) increases.

Answer:

More birds had higher feather density when there was more snowfall. This suggests birds with denser feathers were better at surviving colder conditions.