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': 'Bag of membranes ruptures \nSelect and explain. \nA. Before full dilatation of cervix, B. After full dilatation of cervix, C. After head is engaged, D. With excessive show', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Membranes usually rupture after full dilatation of cervix or sometimes even beyond in second stage', 'role': 'assistant'}]