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
The retention in the cast metal restoration is mainly by: 
Select and explain. 
A. Diverging vertical walls, B. Parallel vertical walls, C. Luting cement, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Cast-metal intracoronal restorations, referred to as inlay restorations, rely on diverging vertical walls that are almost parallel and a luting cement to provide retention of the casting in the tooth.
Sturdevant operative dentistry 7th Edition, Page No:120