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: Unknown
Hemoglobin's affinity for oxygen is increased due to ? 
Select and explain. 
A. An increase in CO2, B. Raise in the temperature, C. Higher value, D. A decrease in 2,3 DPG
D: A decrease in 2,3 DPG
Answer: D: A decrease in 2,3 DPG 
Explanation: ANSWER: D A decrease in 2,3 DPG