The correct answer is:
a neutral and factual text informing readers about the role of the wolf population in Yellowstone National Park.
Explanation: An objective tone in explanatory writing emphasizes neutrality, facts, and information without personal bias or emotional language. This option provides factual information about the wolf population in Yellowstone without expressing personal opinions or experiences, making it an example of an objective tone. In contrast, the other options are more subjective, focusing on personal accounts, persuasive appeals, or emotional experiences, which do not align with the objective tone intended in explanatory writing.