Explanation: an audience is a group of spectators at a public event; listeners or viewers collectively, as in attendance at a theater, speech, or concert. Before a formal audience, we should prepare a formal speech, which should be very correct and serious rather than relaxed and friendly, and usually doesn't have visual aids. From the given options, the only one that would be appropriate for a speech before a formal audience is to include quotes from a well-respected author.
Thank you for serving our country to ensure our freedom and rights! I will always appreciate you and the others who have served. Your sacrifice can never be repaid but your service will never be forgotten.
