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
Bag of membranes ruptures 
Select and explain. 
A. Before full dilatation of cervix, B. After full dilatation of cervix, C. After head is engaged, D. With excessive show
B: After full dilatation of cervix
Answer: B: After full dilatation of cervix 
Explanation: Membranes usually rupture after full dilatation of cervix or sometimes even beyond in second stage