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: Surgery
Commonest cause for hyperparathyroidism is ? 
Select and explain. 
A. Single adenoma, B. Multiple adenomas, C. Single gland hyperplasia, D. Multiple gland Hyperplasia
A: Single adenoma
Answer: A: Single adenoma 
Explanation: Ans. is 'a' i.e., Single adenoma