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: Radiology
[{'content': 'The most common radio-opaque mass at root apex of a vital tooth is due to: \nSelect and explain. \nA. Hypercementosis, B. Condensing osteitis, C. Periapical cemental dysplasia, D. True cementoma', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]