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': 'Which of the following is not useful for coagulation \nSelect and explain. \nA. Plasmin, B. Thrombin, C. Calcium, D. Fibrin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]