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
Predisposing factor for pneumococcal pneumonia 
Select and explain. 
A. CRF, B. Lymphoma, C. Old age, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None