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: Medicine
[{'content': "Most common cause of hyperparathyroidism is - \nSelect and explain. \nA. Solitary adenoma, B. Chief cell hyperplasia, C. Multiple adenoma, D. Werner's syndrome", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]