This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cold Chain in India, Subject name: Social & Preventive Medicine
[{'content': 'How many fully frozen ice packs should a vaccine carrier contain? \nSelect and explain. \nA. 2, B. 4, C. 6, D. 8', 'role': 'user'}, {'content': 'Answer: B \nExplanation: - Vaccine carrier contain 4 fully frozen ice-packs - Day carrier contain 2 fully frozen ice-packs', 'role': 'assistant'}]