The answer is D. The magnitude of the relationship between lead exposure and ADHD is similar to the relationships between lead exposure and conduct disorder as well as between lead exposure and low IQ.

Publication reference : Lead and Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms: a meta-analysis. Goodlad JK et al. Clin Psychol Rev. (2013)
Reference URL: http://www.sciencedirect.com/science/article/pii/S0272735813000123