This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fetal Skull and Maternal Pelvis, Subject name: Gynaecology & Obstetrics
[{'content': 'Definition of crowning - \nSelect and explain. \nA. Biparietal diameter at the inlet of pelvis, B. Biparietal diameter at the ischial spine, C. Biparietal diameter at the vulval outlet, D. Biparietal diameter just outside the vulval outlet', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Biparietal diameter at the vulval outlet o Repeat from previous sessions", 'role': 'assistant'}]