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': 'Dense cortical bone used for implant placement is found\nin: \nSelect and explain. \nA. Anteiror mandible, B. Posterior mandible, C. Anterior maxilla, D. Posterior maxilla', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]