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': 'On stomach washing which poison turns to black on exposure to silver nitrate: \nSelect and explain. \nA. Tik 20, B. Celphos, C. Malathion, D. Arsenic', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Celphos', 'role': 'assistant'}]