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
MC deficient enzyme in Congenital adrenal hyperplasia: March 2013 
Select and explain. 
A. 21-hydroxylase deficiency, B. 18-hydroxylase deficiency, C. 3-beta-hydroxysteroid dehydrogenase deficiency, D. 17-alpha hydroxylase deficiency
A: 21-hydroxylase deficiency
Answer: A: 21-hydroxylase deficiency 
Explanation: Ans. A i.e. 21-hydroxylase deficiency