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
The clot formed is not stable unless extensive cross-linking occurs. This extensive cross-linking of blood clot is done by: 
Select and explain. 
A. Plasmin, B. Thrombin, C. HMWK, D. Factor XIII
D: Factor XIII
Answer: D: Factor XIII 
Explanation: Ans: D. Factor XIIIConversion of fibrinogen into cross-linked fibrin:Thrombin directly conves soluble fibrinogen into fibrin monomers.Fibrin monomers polymerize into an insoluble clot & also amplifies coagulation process - By activating factor XI, factors V & VIII.Also stabilizes secondary hemostatic plug - By activating factor XIII.Factor XIII - Covalently cross-links fibrin.Ref: Robbing 9/e 11 9