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: Pathology
[{'content': "Disease characterized by insidious onset and by an absolute increase in number of circulating RBCs and in total blood volume? \nSelect and explain. \nA. Leukopenia, B. Osler's disease, C. Mediterranean disease, D. Aplastic anaemia", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]