A、Too much eating. B、Too much unhealthy food. C、Too little activities. D、The overweight problem. D

Too much eating. Too much unhealthy food. Too many advertisements for food. Too little activity. Different explanations are offered for Americans’ weight problem—a problem increasingly shared by other countries. (19)Almost 1/5 of American children and teenagers are overweight. (20)Schools have been urged to increase physical education, an important tool for public health. And many have. Yet now comes a study showing an increase in the number of injuries in "phys ed" class. Injuries increased 150% in the last ten years. The study involved injuries treated in hospital emergency departments. Only 2% were serious. The researchers did not try to identify the causes of the increase, but they have some theories. Lara McKenzie from Ohio State University was the lead researcher. (21)She says one possibility is a decrease in the number of school nurses during the period they studied. For example, a study showed that the number of school nurses nationally failed to meet federal guidelines. Schools without a nurse on duty may be more likely to send an injured child to a hospital. (21) Another possible reason for more injuries is a change in the traditional idea of physical education. This "New PE" expands the kinds of sports that are taught. But activities that some schools offer now, like rock climbing walls and skateboarding, can also expand the risks, says Cheryl Richardson. She is with the National Association for Sport and Physical Education. Also, she says not all states require PE teachers to be specially trained. Untrained teachers could be less likely to recognize unsafe conditions.
19. What’s the problem that American children are facing?
20. What measure has been taken to solve Americans’ weight problem?
21. What’s the reason for the increase of school injuries according to the passage?