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
Cast perforated resin retained FPD derives its prime retention from: 
Select and explain. 
A. Mechanical means, B. Chemical means, C. Micro-mechanical means, D. Chemo-mechanical means
A: Mechanical means
Answer: A: Mechanical means 
Explanation: Cast perforated resin-retained fpds (mechanical retention)