The answer is A: A speech to welcome people to a local talent show.
Informal tone, as opposed to formal tone (which is direct and concise), is characterized by a personal and colloquial sense that aims at raising conviviality, a sense of nearness, connection, and familiarity that can breed confidence and trust on the side of the audience so that they can feel comfortable and ready to open up.
The best example of a primary source among these options that you've mentioned is an interview with her dad who is a Vietnam veteran. She can get all the details she needs from a person who was actually there.
