The correct answer is - a. hibernation.
Big portion of the animals living in the alpine biome tend to hibernate during the winter period, and the reasons for that are multiple, like food shortage, very cold weather, and very importantly, there's places where to take shelter and hibernate.
The taiga, on the other hand, comes to be more cruel in this aspect. It is a biome that in general has a food shortage, the winter lasts for most of the year, but the animals do not have any suitable places as to where they can hibernate, so they have to be active all the time.