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
A dead body is having cadaveric lividity of bluish green color. The most likely cause of death is by poisoning due to: AIIMS 06; DNB 10; NEET 13 
Select and explain. 
A. Hydrocyanic acid, B. Hydrogen sulfide, C. Oleander, D. Sodium nitrite
B: Hydrogen sulfide
Answer: B: Hydrogen sulfide 
Explanation: Ans. Hydrogen sulfide