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': 'Most common reason for failure of rest seat in RPD is \nSelect and explain. \nA. Improper rest seat preparation, B. Contaminated metal, C. Distorted occlusal rest, D. Excessive occlusal forces', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]