This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pituitary-Hypothalmic System and Thyroid, Subject name: Pharmacology
[{'content': 'The physical half life of radioactive I131 is: \nSelect and explain. \nA. 8 hrs, B. 8 days, C. 16 days, D. 60 days', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Half life of radioactive I131 is 8 days. It can cause irreversible hypothyroidism. It is contra-indicated in pregnancy.', 'role': 'assistant'}]