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: Surgery
[{'content': 'In Rubber band extraction, extraction of the tooth occurs because of: \nSelect and explain. \nA. Tearing of PDL., B. Necrosis of PDL., C. Both, D. None', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Pressure of elastic leads to ischaemia and hence necrosis of PDL.\nDue to this, tooth becomes mobile and leads to extraction of tooth.', 'role': 'assistant'}]