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': 'The function of vitamin K is: \nSelect and explain. \nA. Thrombin formation, B. Prothrombin formation, C. Fibrin formation, D. Thromboplastin formation', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]