Answer:
Option D, It has destroyed some of the lichens they feed on.
Step-by-step explanation:
During winter, Caribou population depends majorly on arboreal lichens/or lichens which grow on trees or open land in an old forest area. These lichen can survive only in moist air condition with in the deep forest canopies and take long time to form/develop . Any disturbance caused to these forest canopies can cause the lichens to die out thereby making the Caribou species subjected to extreme hunger and hence reduction in their population.
Also the redevelopment of these lichens takes a long time, due to which food become scarce and caribou population reduces.