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': 'Formen of Magendie is the central opening of? \nSelect and explain. \nA. Lateral ventricle, B. 4th ventricle, C. 3rd ventricle, D. None', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., 4th ventricle", 'role': 'assistant'}]