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': 'Hematocrit relates to which of the following: \nSelect and explain. \nA. Total blood volume, B. Total RBC volume, C. Total WBC volume, D. Plasma filtrate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]