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: Anatomy
[{'content': 'Yolk sac is derived from \nSelect and explain. \nA. Hypoblasts, B. Epiblasts, C. Syncytiotrophoblast, D. None', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., HypoblastsThe yolk sac develops from hypoblast cells. By the end of 2nd week the lower half of primary yalk sac pinches off to form definitive yolk sac, while a second wave of hypoblast cells form inner lining of definitive yolk sac.", 'role': 'assistant'}]