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
Most common cause of hyperparathyroidism: 
Select and explain. 
A. latrogenic, B. Medullary carcinoma thyroid, C. Parathyroid adenoma, D. Parathyroid hyperplasia
C: Parathyroid adenoma
Answer: C: Parathyroid adenoma 
Explanation: Answer is C (Parathyroid Adenoma): The most common cause of primary hyperparathyroidism is a single /solitary parathyroid adenoma.