Researchers who followed a large, representative sample of U. S. youths from ages 9 to 17 found that . A. daily free-time physical activity declined with age, more so for girls than boys
B. at every age, a majority of participants engaged in regular exercise
C. outside of school hours daily free-time physical activity increased for both sexes until age 13, then declined
D. throughout adolescence, girls exceeded boys in regular daily exercise