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
Black pigmented bacteroides release ______ as agent
responsible for unpleasant smell of breath. 
Select and explain. 
A. Methyl mercaptan, B. Hydrogen sulphide, C. Dimethyl sulphide, D. Propionic acid
B: Hydrogen sulphide
Answer: B: Hydrogen sulphide 
Explanation: None