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
Which of the following coagulation factor causes cross linking and stabilization of clot? 
Select and explain. 
A. Factor XIII, B. Thrombin, C. Factor VIII, D. Factor IX
A: Factor XIII
Answer: A: Factor XIII 
Explanation: Thrombin activates factor XIII (fibrin stabilizing factor) to factor XIIIa, which forms cross links and thereby stabilizes the clot.