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': 'Irregular opaque areas are found on radiographs of lower anterior teeth, the teeth are VITAL the cause may be: \nSelect and explain. \nA. Subgingival calculus, B. Cementoma, C. Condensing osteitis, D. Chronic apical periodontitis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]