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
Death due to which poison causes postmortem staning of cherry-red colour 
Select and explain. 
A. Carbon monoxide, B. Aniline, C. Phosphorus, D. Nitrites
A: Carbon monoxide
Answer: A: Carbon monoxide 
Explanation: None