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
Which of the following OPV ls are usable? 
Select and explain. 
A. Only 1, B. Only 1, 2, C. Only 1, 2, 3, D. Only 3, 4
B: Only 1, 2
Answer: B: Only 1, 2 
Explanation: 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).