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': 'Commonest cause of non-engagement at term, in priori is : \nSelect and explain. \nA. CPD, B. Hydramnios, C. Brow presentation, D. Breech', 'role': 'user'}, {'content': 'Answer: A \nExplanation: CPD', 'role': 'assistant'}]