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: Medicine
[{'content': 'Predisposing factor for pneumococal pneumoniaa) CRFb) Lymphoma c) Thalassemiad) Cystic fibrosis \nSelect and explain. \nA. abc, B. bc, C. acd, D. bcd', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]