This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'Which of the following is the engaging diameter in the fetus in left occiput anterior (LOA) position: \nSelect and explain. \nA. Suboccipito - bregmatic, B. Mento-veical, C. Sub-Mento bregmatic, D. Sterno-Bregmatic', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Position of Head Presentation Engaging diameter Well flexed head Veex presentation Sub-Occipito bregmatic, 9.5 cms Deflexed head Sinciput presentation Occipito-frontal , 11.5cms Paial extended Brow presentation Mento veex, 14 cms Fully extended head Face presentation Submentobregmatic ,9.5cms or submentoveical 10 cms', 'role': 'assistant'}]