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
The commonest cause of primary hyperparathyroidism is - 
Select and explain. 
A. Carcinoma parathyroid, B. Solitary adenoma of parathyroid, C. Chronic renal failure, D. Hyperplasia of the parathyroid
B: Solitary adenoma of parathyroid
Answer: B: Solitary adenoma of parathyroid 
Explanation: None