This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
True statement about primary hyperparathyroidism- 
Select and explain. 
A. Adenoma commonest cause, B. serum calcium, C. Surgery if biochemical finding is abnormal in asymptomatic patient, D. MIBG isotope is useful in localization of tumor
A: Adenoma commonest cause
Answer: A: Adenoma commonest cause 
Explanation: Solitary adenoma common cause around 80% of primary hyperparathyroidism Ref - ( Harrison 17 pg 2380)