This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abnormal labor, Subject name: Gynaecology & Obstetrics
[{'content': 'Commonest cause of non-engaged head in primi at term is \nSelect and explain. \nA. CPD, B. Hydramnios, C. Brow presentation, D. Breech presentation', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Causes of Obstructed labour : CPD Contracted pelvis Cervical dystocia Transverse lie Brow presentation Hydrocephalus Big baby Compound presentation Locked twins Ref: Dutta Obs 9e pg 379.', 'role': 'assistant'}]