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
Loose fibrin accumulated in tight clot in coagulation pathway by factor ? 
Select and explain. 
A. X, B. XI, C. XII, D. XIII
D: XIII
Answer: D: XIII 
Explanation: Ans. is 'd' i.e., XIII Loose (soluble) fibrin is conveed to insuluble fibrin by thrombin and XIIIa.