Final answer:
The best example that would support the student's claim that recess is important for high school students is research from the U.S. Dept. of Health and Human Services highlighting the benefits of physical activity.
Step-by-step explanation:
The best example that would support the student's claim that recess is important for high school students is option C, which is research from the U.S. Dept. of Health and Human Services highlighting the benefits of physical activity. This research would provide evidence-based information about how physical activity, such as recess, can relieve stress and stimulate the brain.