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: Forensic Medicine
[{'content': "Kunkel's test is done demonstrate the presence of --in blood. \nSelect and explain. \nA. Lead, B. CuSO4, C. CO, D. Dhatura", 'role': 'user'}, {'content': 'Answer: C \nExplanation: CO', 'role': 'assistant'}]