Which of the Following Is True of Recent Studies on Adolescents

Which of the following is true of recent studies on adolescents and masturbation?

A) Kinsey's report on adolescent masturbation shows that girls don't masturbate.
B) Adolescents tend to masturbate at an earlier age now than they did in the past.
C) Frequent masturbation was believed to be beneficial in the early 20^th century.
D) Masturbation in adolescents is uncommon and a sign of abnormal behavior.