The best elaboration for the topics discussed among the given situations is:
Riley wants to tell older teenagers why young people need to vote. To elaborate, she could include facts that show how many younger people are registered to vote in the upcoming election.
This response provides relevant facts that can strengthen Riley's argument, offering concrete evidence that adds depth to her message about the importance of voting among young people. The other examples either rely on personal anecdotes or subjective opinions, which do not provide as strong an elaboration as factual evidence does in this context.