72   Which of the following is not a true statement with respect to theorized etiologies of ADHD?

A. Psychosocial factors do not appear to contribute to the development of ADHD.

B. Some literature suggests that prenatal exposure to winter infection during the first trimester of pregnancy leads to ADHD

C. Biological parents of children with ADHD have a higher incidence of the disorder than adoptive parents

D. Overall, no clear-cut evidence supports a single neurotransmitter in the development of ADHD