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 biological anticoagulant is: \nSelect and explain. \nA. EDTA, B. Sodium citrate, C. Hirudine, D. Double oxalate mixture', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]