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': 'Odontoclasts for tooth resorption are mainly derived from: \nSelect and explain. \nA. PDL., B. Cementum., C. Bone., D. Dentin.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Odontoclasts for tooth resorption are mainly derived from PDL', 'role': 'assistant'}]