This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Storage of vaccines, Subject name: Pediatrics
[{'content': 'An OPV l shows this symbol on it. What does it indicate? \nSelect and explain. \nA. The vaccine has reached its expiry date, B. The vaccine has not been stored properly, C. The vaccine l is empty, D. Use the vaccine if expiry date not reached', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The pictures below show the interpretation of vaccine l monitor on the OPV vaccine l: - If color of inside square lighter than outside circle - We can use the vaccine - It is heat sensitive label that indicates cumulative heat exposure over time.', 'role': 'assistant'}]