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': 'Beginning of eruption of permanent tooth starts: \nSelect and explain. \nA. After completion of root, B. When apical third root is still to be formed, C. When half of the root is still to be formed, D. When root formation starts', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]