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: Pediatrics
[{'content': 'Congenital Adrenal Hyperplasia is due to deficiency of: \nSelect and explain. \nA. 21 beta hydroxylase, B. 17 alpha hydroxylase, C. 5 alpha reductase, D. 17 beta reductase', 'role': 'user'}, {'content': "Answer: A \nExplanation: a. 21 beta hydroxylase(Ref: Nelson's 20/e p 2714-2723, Ghai 8/e p 526-527)Most common cause of Congenital Adrenal Hyperplasia is 21 beta hydroxylase deficiency.", 'role': 'assistant'}]