This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Anatomy
[{'content': 'Commonest cause of non engagement at term, in primi is: \nSelect and explain. \nA. CPD, B. Hydramnios, C. Brow presentation, D. Breech', 'role': 'user'}, {'content': "Answer: A \nExplanation: In primi's the most common cause of non engagement at term is deflexed head or occipitoposterior position followed by cephalopelvic dispropoion. Ref: Datta Obs 9e pg 330.", 'role': 'assistant'}]