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': 'In the pre-school stage what % of the children show thumb-sucking \nSelect and explain. \nA. Less than 10%, B. 10-20%, C. More than 50%, D. all children', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]