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: Dental
[{'content': 'The principal characteristics of attention-deficit/hyperactivity disorder are all of the following except one. Which one is the exception? \nSelect and explain. \nA. Inattention, B. Mental retardation, C. Hyperactivity, D. Impulsivity', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Inattention and hyperactivity/impulsivity are the key behaviors of ADHD. Some people with ADHD only have problems with one of the behaviors, while others have both inattention and hyperactivity-impulsivity. Most children have the combined type of ADHD.\nIn preschool, the most common ADHD symptom is hyperactivity.\nIt is normal to have some inattention, unfocused motor activity, and impulsivity, but for people with ADHD, these behaviors:\n\nAre more severe\nOccur more often\nInterfere with or reduce the quality of how they function socially, at school, or in a job.', 'role': 'assistant'}]