The correct answer is: The school board should include a student member to represent youths' opinions.
This is the only sentence that tries to presuade the audience to do something specific, in this case, include a student member. Let's remeber that to persuade is to make an attempt to make a person behave in a manner or embrace a point of view, one that was not shared. By using the word should: "used to say or ask what is the correct or best thing to do" the author tries to indicate the audience what thing is the best to do. It also gives a reason for his claim "to represent youths' opinions", this is what makes it strong, it gives osme evidence of his way of thinking.
The other options only give information about the school board, they don't try to persuade anyone to anything. They can be used to support the main claim in a persuasive speech.
