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
Serum contains all the clotting factors, except 
Select and explain. 
A. Plasma thromboplastin, B. Labile factor, C. Hageman factor, D. Christmas factor
B: Labile factor
Answer: B: Labile factor 
Explanation: If whole blood is allowed to clot and the clot is removed, the remaining fluid is called serum. Serum has essentially the same composition as plasma, except that:

Fibrinogen (factor I) and clotting factors II, V, and VIII have been removed and
Has higher serotonin content, because of the breakdown of platelets during clotting.

Also, know that factor 5 is called as labile factor.