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: Dental
[{'content': 'Impression tray for preliminary edentulous impression should be selected such that the edentulous stock tray is: \nSelect and explain. \nA. 5 mm larger than outside surface of ridge, B. 7 mm larger than outside surface of ridge, C. 3 mm larger than outside surface of ridge, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: An edentulous tray should be selected, such that it provides for 5mm of bulk of material over entire basal seat area.', 'role': 'assistant'}]