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
Hypothyroidism in sub Himalayan is due to? 
Select and explain. 
A. Iron, B. Iodine, C. Copper, D. Selenium
B: Iodine
Answer: B: Iodine 
Explanation: ANSWER: (B) IodineREF: Park 20th ed p. 540'Iodine deficiency in sub himalayan terrain leads to endemic goitre and hypothyroidism"