Final answer:
The student should ask about the rules of the La Tomatina festival.
Step-by-step explanation:
The best question for a student to ask in response to the speaker's comment that "La Tomatina became an annual tradition with its own set of simple rules" would be: What are the rules of the La Tomatina festival? This question directly addresses the speaker's comment and seeks to learn more about the specific rules of the festival.
Learn more about La Tomatina festival rules