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: Surgery
[{'content': 'According to Cawood and Howell, a depression with cup shaped surface of edentulous atrophic maxilla is classified as \nSelect and explain. \nA. Class III, B. Class IV, C. Class V, D. Class VI', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]