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
[{'content': 'All of the following are essential features of attention deficit hyperactivity disease (ADHD) except: \nSelect and explain. \nA. Lack of concentration, B. Impulsivity, C. Mental retardation, D. Hyperactivity', 'role': 'user'}, {'content': 'Answer: C \nExplanation: ADHD children will not have mental retardation. Ref: Text Book of Pediatrics By Nelson, 17th Edition, Pages 107-108', 'role': 'assistant'}]