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: Medicine
[{'content': "Polycythemia may be a features of all of the following except \nSelect and explain. \nA. Gastric carcinoma, B. Hepatoma, C. Cushing's syndrome, D. Hypemephroma", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]