Mark the letter A, B, Cor D on your answer sheet to indicate the best arrangement of utterances or sentences to make a meaningful exchange or text in each of the following questions from 13 to 17.

a. Initially, many were skeptical about how this would affect the ecosystem.
b. The reintroduction of wolves to Yellowstone National Park has become a classic example of successful conservation.
c. Over time, the wolves' presence helped control the elk population.
d. This led to the regeneration of vegetation and the return of various species.
e. Today, the park serves as a model for ecosystem restoration worldwide.