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
Hemophilia B is due to: 
Select and explain. 
A. Factor VII deficiency, B. Factor IX deficiency, C. Platelet deficiency, D. Vit C deficiency
B: Factor IX deficiency
Answer: B: Factor IX deficiency 
Explanation: None