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': 'Test for detection or old blood stain is - \nSelect and explain. \nA. Gel diffusion, B. Precipitin test, C. Absorption elution test, D. Benzidine test', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Amongst the given options, only benzidine test is used to detect the nature of stain, i.e. whether it is blood or not.', 'role': 'assistant'}]