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 - \nSelect and explain. \nA. Iatrogenic, B. Medullary carcinoma thyroid, C. Parathyroid adenoma, D. Parathyroid hyperplasia', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]