This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Which of the following is not a naturally occurring anticoagulant in the body? \nSelect and explain. \nA. Protien C, B. Protien S, C. Antithrombin III, D. Von Willebrand factor', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Antithrombin 3 is a circulating protease inhibitor that binds to serine proteases blocking their activity as a clotting factor. Activated protein c along with cofactor protein s inactivates factors 5 and 8 and inactivates inhibitors of tissue plasminogen activator increasing formation of plasmin.Von Willebrand factor helps in platelet aggregationRef: Ganong&;s Review of medical physiology, 24th edition.Pg no.78,566', 'role': 'assistant'}]