Answer:
For years, the elk population grew rapidly until the reintroduction of wolves to the park in 1995.
Step-by-step explanation:
An interaction is when two or more things encounter or meet together, come together, or get involved. The action occurs between two or more objects which will result in an effect of one kind or anything.
In the given passage, the interaction is seen in the sentence "For years, the elk population grew rapidly until the reintroduction of wolves to the park in 1995." This sentence describes or mentions the "interaction" of the elks and wolves, brought together and in one space/ location.
Thus, the correct answer is the fourth or last option.