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: Pathology
Most common cause of congenital adrenal hyperplasia: Maharashtra 10 
Select and explain. 
A. 21-Hydroxylase deficiency, B. 11-Hydroxylase deficiency, C. 17-a-Hydroxylase deficiency, D. 3-P-Hydroxy dehydrogenase deficiency
A: 21-Hydroxylase deficiency
Answer: A: 21-Hydroxylase deficiency 
Explanation: Ans. 21-Hydroxylase deficiency