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: Physiology
[{'content': 'Normal CD4 cell count is: \nSelect and explain. \nA. 500/cu.mm, B. 1000/cu.mm, C. 200/cu.mm, D. 700/cu.mm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]