The answer is B) wolves consuming populations of elk and reducing the population to its original size within the park
When wolves were eliminated, the elk population grew out of control. This meant less food for an overpopulated amount of elk. When the wolves were brought back, the elk population was controlled and became its original size.
A is not the answer because, when introducing a predator back to the same area with overpopulated elk, the elk population would not increase.
C is not the answer because there is too many elk for the wolf population to go down. When there is more food supply for wolves, the wolf population would reduce the amount of elk instead of the wolves population to decrease.
D is not the answer because there would be no newly established trees when the elk over ate their food supply. There would be less elk after the introduction of wolves, so they wouldn't consume larger areas due to decrease in population.