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': 'Cast perforated resin retained FPD derives its prime retention from: \nSelect and explain. \nA. Mechanical means, B. Chemical means, C. Micro-mechanical means, D. Chemo-mechanical means', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Cast perforated resin-retained fpds (mechanical retention)', 'role': 'assistant'}]