This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Pathology
[{'content': 'In which of the following conditions that cause polycythemia is the serum erythropoietin extremely low - \nSelect and explain. \nA. Dehydration, B. Renal cell carcinoma, C. Renal cell carcinoma, D. Polycythemia vera', 'role': 'user'}, {'content': 'Answer: D \nExplanation: In polycythemia vera unlike secondary polycythemia erythropoietin levels in serum and urine are reduced. Reference textbook of Pathology 7th edition author Harsha Mohan page number 339', 'role': 'assistant'}]