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': 'Which stage is characterized by beginning of mineralization and root formation: \nSelect and explain. \nA. Advanced Bell Stage., B. Early Bell Stage., C. Bus Stage ., D. Cap Stage.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]