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': 'Vaccum extraction is done when : \nSelect and explain. \nA. Cervix dilated more than 8 cm, B. Persistent occipito posterior, C. Deep transverse arrest, D. All', 'role': 'user'}, {'content': 'Answer: D \nExplanation: All', 'role': 'assistant'}]