[单项选择]Common sense would tell us that physically active children may be more likely to become active and healthy adults．73 In the United States，elementary and middle schools are advised to give students two and a half hours of ohvsical activity a week．That is what the Centers for Disease Control and Prevention and the American Heart Association l’ecommend (推荐)．They say high schools should provide about four hours of physical activity each week．Yet many schools across the country have reduced their physical education programs．Criticism of the cuts has led in some places to efforts to give students more time for exercise，not less．
The future health of Americans may depend on it．Just this week，a study reported that life expectancy(预期寿命)has fallen or is no longer increasing in some parts of the United States．The situation 1s worst among poor people in the southern states．and especially women．Public health researchers say it is largely the result ofincreases in obesity(肥胖)，smoking and high b
A. Because difierent schools set up difrerent physical education programs．
B. Because the physical activity of children will influence their health in adulthood．
C. Because nowadays children spend too much time on their studies．
D. Because only four percent of elementary schools provided daily physical education．