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: Unknown
The primitive gut is a derivative of - 
Select and explain. 
A. Yolk sac, B. Amniotic cavity, C. Allantoic cavity, D. Coelum
A: Yolk sac
Answer: A: Yolk sac 
Explanation: Ans: A