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: Dental
[{'content': 'Black pigmented bacteroides release ______ as agent\nresponsible for unpleasant smell of breath. \nSelect and explain. \nA. Methyl mercaptan, B. Hydrogen sulphide, C. Dimethyl sulphide, D. Propionic acid', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]