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: Physiology
Christmas disease is due to the deficiency of the following clotting factor: 
Select and explain. 
A. Factor 8, B. Factor 9, C. Factor 11, D. Factor 12
B: Factor 9
Answer: B: Factor 9 
Explanation: Haemophilia B or Christmas disease is due to the deﬁciency of factor 9.