This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parathyroid, Subject name: Medicine
[{'content': 'The commonest cause of primary hyperparathyroidism is : \nSelect and explain. \nA. Carcinoma parathyroid, B. Solitary adenoma of parathyroid, C. Chronic renal failure, D. Hyperplasia of the parathyroid', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' Parathyroid adenoma (Ref Harrison, 17/e, p 2380 & 16/e, p 2252 (15/e, p 2210)).Most common cause of primary hyperparathyroidism is parathyroid adenoma.", 'role': 'assistant'}]