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': 'The primary germ layer endoderm is derived from: \nSelect and explain. \nA. Embryonal disc, B. Yolk sac, C. Amniotic cavity, D. Placenta', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]