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: Medicine
[{'content': 'Blood flow in hemodialysis machine \nSelect and explain. \nA. 100-200 ml/min, B. 300-500 ml/min, C. 700-800 ml/min, D. >1000 ml/min', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Blood flow -\xa0300-500 ml/min.\nDialysate - 500-800 ml/min in opposite direction.', 'role': 'assistant'}]