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': 'Regeneration of lost periodontium involves \nSelect and explain. \nA. Healing by new attachment formation, B. Healing by long junctional epithelium formation, C. Healing by re-attachment, D. Healing by scar formation', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]