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': 'Which of the following OPV ls are usable? \nSelect and explain. \nA. Only 1, B. Only 1, 2, C. Only 1, 2, 3, D. Only 3, 4', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Rules for VVM use in India Rules 1: If the inner square is lighter than the outer circle, the vaccine may be used (Vials 1, 2) Rules 2: If the inner square is the color as, or darker than, the outer circle, the vaccine must not be used (Vials 3, 4).', 'role': 'assistant'}]