This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: general microbiology, Subject name: Microbiology
[{'content': 'Shelf life of CPD blood is \nSelect and explain. \nA. 3 weeks, B. 6 weeks, C. 9 weeks, D. 12 weeks', 'role': 'user'}, {'content': 'Answer: A \nExplanation: CPD - shelf life of blood stored in CPD stored at 2 to 4C is 21 days CPD:Citric acid Phosphate dextrose', 'role': 'assistant'}]