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': 'A 32 year old high altitude mountaineer is observed to have a hematocrit of 70%. Which of the following represents the most likely cause/explanation \nSelect and explain. \nA. Polycythemia with increased red cell mass, B. Relative polycythemia due to dehydration, C. Polycythemia due to hemoconcentration, D. Polycythemia with high altitude pulmonary edema', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Erythropoietin secretion increases promptly on ascent to high altitude. The increase in circulating red blood cells triggered by the erythropoietin\xa0 begins\xa0in\xa0 2-3\xa0days\xa0and\xa0is sustained as long as the individual remains at high altitude.', 'role': 'assistant'}]