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': 'Most unourable presentation for vaginal delivery is / delivery not possible per vaginum is : \nSelect and explain. \nA. Mento posterior, B. Mento anterior, C. Occipito posterior, D. Deep transverse arrest', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Mento posterior', 'role': 'assistant'}]