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': 'Which of the following poisonings causes the blood to become cherry red? \nSelect and explain. \nA. Cyanide, B. H2S, C. Potassium per chlorate, D. Nitrite', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Cyanide stops respiration at mitochondrial level so the O2 in the blood is not used and hence a high saturation of O2 in the blood gives it the bright red color. H2S changes the red blood pigment; blood turns brown to olive in color. In potassium per chlorate poisoning, the blood is of a chocolate color. Nitrite poisoning causes methemoglobinemia and anemic anoxia. Signs are dyspnea and coffee color of mucosae and blood.', 'role': 'assistant'}]