Answer:
A.) .Birds with white feathers in areas without winter snow will be easier for predators to find. Over time this could lead to white-tailed ptarmigans that have brown feathers throughout the year.
Explanation: This seems to make the most sense. The birds with the Brown feathers are more likely to survive and reproduce so they will pass the trait of retaining Brown feathers year round to their offspring. This is likely to continue as long as there is no snow in the winter environment.