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': 'Gastric lavage turns black in presence of Silver nitrate, most probable poisoning was: \nSelect and explain. \nA. Celphos, B. Malathion, C. Organophosphorus, D. Parathion', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. Celphos', 'role': 'assistant'}]