This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'How long can blood be stored with CPD -A - \nSelect and explain. \nA. 21 days, B. 28 days, C. 35 days, D. 42 days', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]