This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Embryology 1, Subject name: Anatomy
Which of the following does not pass through the primitive umbilical ring? 
Select and explain. 
A. Allantois, B. Amnion, C. Yolk sac, D. Connecting stalk
B: Amnion
Answer: B: Amnion 
Explanation: The amnion does not pass through the primitive umbilical ring. As craniocaudal folding occurs, the amnion becomes the outer covering of the umbilical cord.