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
What is the investigation of choice for blood grouping in old blood stain on cloth 
Select and explain. 
A. Benzidine test, B. Acid dilution test, C. Haemin crystal test, D. Precipitin test
B: Acid dilution test
Answer: B: Acid dilution test 
Explanation: B i.e. Acid dilution test