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': 'The most common cause of ambiguous genitalia in a newborn is – \nSelect and explain. \nA. 21 hydroxylase deficinece, B. 11 β – hydroxylase deficiency, C. 17 α – hydroxyalse deficiency, D. 3 β – hydroxysteroid deficiency', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Congenital adrenal hyperplasia due to classic 21-Hydroxylase deficiency is the most common cause of ambiguous genitalia in the newborn. Virilization is apparent at birth in the female and within the first 2-3 years of life in the male.', 'role': 'assistant'}]