B, after long-term physical exercise and physical labor, it can strengthen the contractility of respiratory muscles, expand the range of chest activities and increase the number of alveoli involved in gas exchange. It leads to an increase in vital capacity and enhanced respiratory function, which does not meet the meaning of the question.
C, people who often participate in physical exercise, developed myocardium, strong pulse, stroke output than the average person, heart rate is slower than the average person in a quiet state. Therefore, it does not meet the problem;
D. Exercise can promote blood circulation and strengthen the delivery of nutrients, so it can improve the nutrition of the brain. However, the longer you exercise, the better your health will be. If the amount of exercise is too large, it will easily increase the burden on body organs and even cause damage, so exercise should be moderate.
So choose d