This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thyroid, Subject name: Medicine
[{'content': 'Hypothyroidism in sub Himalayan is due to? \nSelect and explain. \nA. Iron, B. Iodine, C. Copper, D. Selenium', 'role': 'user'}, {'content': 'Answer: B \nExplanation: ANSWER: (B) IodineREF: Park 20th ed p. 540\'Iodine deficiency in sub himalayan terrain leads to endemic goitre and hypothyroidism"', 'role': 'assistant'}]