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
Halitosis is primarily because of: 
Select and explain. 
A. Hydrogen sulfide, B. Alkaline phosphates, C. Trypsine like enzymes, D. Collagenase enzymes
A: Hydrogen sulfide
Answer: A: Hydrogen sulfide 
Explanation: None