This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
All of the following are essential features of attention deficit hyperactivity disease (ADHD) except: 
Select and explain. 
A. Lack of concentration, B. Impulsivity, C. Mental retardation, D. Hyperactivity
C: Mental retardation
Answer: C: Mental retardation 
Explanation: ADHD children will not have mental retardation. Ref: Text Book of Pediatrics By Nelson, 17th Edition, Pages 107-108