A、Because being active is the cause of higher grades. B、Because the amount of activity required is just right. C、Because they he

Physical activity may help students do better in their classes. The research comes as educators in some countries are reducing time for activities like physical education. They are using the time instead for academic subjects like math and reading.
    Researchers at VU University Medical Center in Amsterdam reviewed the results of fourteen studies. Twelve were from the United States, one from Canada and one from South Africa. The studies appeared between nineteen ninety-seven and two thousand and nine. They included more than fifty-five thousand children, aged six to eighteen.
    Researcher Amika Singh says the studies showed a link between physical activity and scores on subjects such as math, English and reading, and concluded that being physically active is beneficial for academic performance.
    Ms. Singh offers some possible explanations. There are, first, physiological explanations, like more blood flow, and so more oxygen to the brain. Being physically active means there are more hormones that make your stress level lower and your mood improved, which means you also perform better. Also, students involved in organized sports learn rules and how to follow them. This could improve their classroom behavior and help them keep their mind on their work.
    The study leaves some questions unanswered, however. Ms. Singh says it is not possible to say whether the amount or kind of activity affected the level of academic improvement. This is because of differences among the studies.
    Also, they were mostly observational studies. An observational study is where researchers do not do controlled comparisons. They only describe what they observe. So they might observe a link that students who are more active often have better grades. But that does not necessarily mean being active was the cause of those higher grades.
    Still, the general finding was that physically active kids are more likely to do better in school. Ms. Singh says schools should consider that finding before they cut physical education programs.
Q13: Why do educators in some countries cut physical education programs?
Q14: Why are organized sports beneficial for academic performance?
Q15: Which of the following is one of the unanswered questions?