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
Most common reason for failure of rest seat in RPD is 
Select and explain. 
A. Improper rest seat preparation, B. Contaminated metal, C. Distorted occlusal rest, D. Excessive occlusal forces
A: Improper rest seat preparation
Answer: A: Improper rest seat preparation 
Explanation: None