Regular exercise not only lays the foundation for children's health, but may also earn a higher income in adulthood. Finnish scholars found in a study that began in 1980 and lasted 30 years that at the age of 9 People who regularly participate in physical exercise at age 12 and 15 increase their average income by 12% to 25% over a 10-year period. This association was specific to the male group, and no such association was observed in the female group. If one of the following is true, which best supports the above conclusion? ['The government should provide equal opportunities for children of different economic and social backgrounds to participate in sports activities.', 'Sports-loving college boys have advantages in salary and employment after graduation.', 'Many previous studies have shown that adult physical activity is directly proportional to income.', 'Livelihoods have not survived since the retirement of many sports champions around the world.']