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
A common cause of Primary hyperparathyroidism is: 
Select and explain. 
A. Multiple parathyroid adenomas, B. Solitary parathyroid adenoma, C. Adrenal hyperplasia, D. Ectopic PTH production
B: Solitary parathyroid adenoma
Answer: B: Solitary parathyroid adenoma 
Explanation: Answer is B (Solitary parathyroid adenoma) : The most common cause of primary hyperparathyroidism is a parathyroid adenoma. A single/solitary abnormal gland is the cause in approximately 80% of patients - Harrison The abnormality of the gland is usually a benign neoplasm or 'adenoma' and rarely a parathyroid carcinoma