GMAT Critical Reasoning (CR) | A high percentage of injuries to the anterior cruciate ligament (ACL)

The credited answer is (B). If football player who have a higher tendency toward ACL injury drop out of football before the professional level, the football players who make it to the NFL will have lower tendencies to suffer ACL injuries. The previous year of playing the sport would provide a "weeding" effect, separating out the folks predisposed to ACL injury. Other athletic activities, such as gymnastics, would not have a similar weeding effect. so this would make the NFL stand out