This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Vaccine which requires most stringent condition for storage:(1991) \nSelect and explain. \nA. DPT, B. OPV, C. BCG, D. TT', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans: bRef: Park, 17th ed, p. 93 & 18th ed, p. 99', 'role': 'assistant'}]