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
Impression tray for preliminary edentulous impression should be selected such that the edentulous stock tray is: 
Select and explain. 
A. 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
A: 5 mm larger than outside surface of ridge
Answer: A: 5 mm larger than outside surface of ridge 
Explanation: An edentulous tray should be selected, such that it provides for 5mm of bulk of material over entire basal seat area.