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
Test for detection of old blood stain is 
Select and explain. 
A. Gel diffusion, B. Precipitin test, C. Absorption elution test, D. Benzidine test
D: Benzidine test
Answer: D: Benzidine test 
Explanation: D i.e. Benzidine test