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
[{'content': 'Delay in blood coagulation results from \nSelect and explain. \nA. Human thrombin, B. Heparin, C. Ferric chloride, D. Vit-K', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]