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
[{'content': 'Commonest cause of Cushings syndrome is - \nSelect and explain. \nA. Adrenal adenoma, B. Carcinoma, C. Hyperplasia, D. Atrophy', 'role': 'user'}, {'content': 'Answer: C \nExplanation: "In most cases, the cause is bilateral adrenal hyperplasia due to hypersecretion of pituitary ACTH or ectopic production of ACTH by a nonpituitary source."- Harrison', 'role': 'assistant'}]