The idea that best indicates that one of the purposes of the author of It's Our World, Too!: Young People Who Are Making a Difference is to persuade is:
The crowd applauds the students for writing the letter that was read at the football game.
This moment suggests a positive response and validation from the community, which can be interpreted as a persuasive element, encouraging more young people to take action and make a difference. It highlights the impact of activism and the support it can generate, which aligns with the book's purpose of motivating and inspiring young readers.