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: Gynaecology & Obstetrics
[{'content': 'The blebs of vaginitis emphasematosa contains: \nSelect and explain. \nA. H2S, B. H2, C. NO2, D. CO2', 'role': 'user'}, {'content': 'Answer: D \nExplanation: CO2', 'role': 'assistant'}]