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 hyperactive disease (AD ) except – \nSelect and explain. \nA. Lack of concentration, B. Impulsivity, C. Mental retardation, D. Hyperactivity', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]