Too much eating．Too many unhealthy foods．Too many ads for food．Too few activities．Different reasons are given for America's weight problem---a problem increasingly shared by other countries．Almost one-fifth of American children and teenagers are overweight．

Schools have been asked to increase physical education，an important tool for public health．However，a recent study has shown an increase in the number of injuries in P．E．classes．

Researchers say one possible reason for this is a decrease in the number of school nurses．Schools without a nurse on duty may be more likely to send an injured child to a hospital．

Another possible reason for more injuries is a change in the traditional idea of physical education．This"New P．E．"expands the kinds of sports that are taught．But activities that some schools offer now，like rock climbing and skateboarding，can also increase the risks，says Cheryl Richardson，who is with the National Association for Sport and Physical Education（NASPE）．

She also says not all states require P．E．teachers to be specially trained．Untrained teachers could be less likely to recognize unsafe conditions．

Cheryl Richardson points to one of the study's findings-that injuries are often the result of contact with a person or a structure．This tells her that the teachers were not giving each student enough space to move around safely．

Six activities produced seventy percent of all injuries：running，basketball，football，volleyball，rugby and gymnastics．

The researchers say larger class sizes are another possible reason for the increase in injuries．Larger classes can mean less supervision（监督）．The National Association for Sport and Physical Education says twenty to thirty students in a P．E．class should be the limit．

32．What does the passage mainly discuss？___

A．What leads to the weight problem in America．

B．Whether students should have more P．E．classes．

C．Wh