Which of the following statements is true about the prevalence of attention-deficit/hyperactivity disorder (ADHD) ?

A) Epidemiological studies indicate that 20 percent of children develop ADHD.
B) Boys are more likely than girls to develop ADHD in childhood and early adolescence.
C) Girls with ADHD tend to have more disruptive behavior than boys with ADHD.
D) The percentage of children diagnosed with ADHD is much greater in the United States than in other countries.