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: Social & Preventive Medicine
What is Grafenbers's Ring 
Select and explain. 
A. Vaginal Pessary to prevent prolapse of uterus, B. I Generation IUD, C. A mechanical barrier to prevent pregnancy, D. None of the above
B: I Generation IUD
Answer: B: I Generation IUD 
Explanation: None