This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood Bank & Transfusion Therapy, Subject name: Medicine
[{'content': 'Shelf life of blood in a blood bank in CPDA buffer: \nSelect and explain. \nA. 21 days, B. 30 days, C. 35 days, D. 42 days', 'role': 'user'}, {'content': 'Answer: C \nExplanation: CPDA is Citrate-Phosphate-Dextrose buffer supplemented with adenine. The shelf life of RBC concentrates in CPDA is 35 days. In CPD buffer life span is 28 days.', 'role': 'assistant'}]