Final answer:
The subject of this question is Health. The question is asking about the exercise habits of American adults over the past 15 years.
Step-by-step explanation:
The subject of this question is Health. The question is asking about the exercise habits of American adults over the past 15 years. The data provided shows the percentages of adults who reported exercising for 30 or more minutes at least three times per week during each year. The information referenced in the question emphasizes the health benefits of regular exercise and provides recommendations for the amount and type of exercise adults should engage in for optimal health.