This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thyroid disorders, Subject name: Pediatrics
[{'content': "Most common preventable cause of mental retardation:- \nSelect and explain. \nA. Down's syndrome, B. Congenital hypothyroidism, C. Rett's syndrome, D. Fragile x syndrome", 'role': 'user'}, {'content': 'Answer: B \nExplanation: - Congenital hypothyroidism is the M.C preventable cause of mental retardation - In India incidence is 1:1000 - Most common cause of congenital hypothyroidism is thyroid dysgenesis. - Most common cause of congenital hypothyroidism with goitre- Thyroid dyshormonogenesis.', 'role': 'assistant'}]