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: Pediatrics
[{'content': 'MC deficient enzyme in Congenital adrenal hyperplasia: March 2013 \nSelect and explain. \nA. 21-hydroxylase deficiency, B. 18-hydroxylase deficiency, C. 3-beta-hydroxysteroid dehydrogenase deficiency, D. 17-alpha hydroxylase deficiency', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A i.e. 21-hydroxylase deficiency', 'role': 'assistant'}]