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 appliance used to treat thumbsucking: \nSelect and explain. \nA. Crib appliance, B. Frankel appliance, C. Bionator, D. Activator', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]