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': 'What is the investigation of choice for blood grouping in old blood stain on cloth \nSelect and explain. \nA. Benzidine test, B. Acid dilution test, C. Haemin crystal test, D. Precipitin test', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Acid dilution test', 'role': 'assistant'}]