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
Main cause of RPD failure is: 
Select and explain. 
A. Improper clasp design, B. Insufficient contact of teeth, C. Insufficient contact of teeth and improper clasp design, D. None of the above
C: Insufficient contact of teeth and improper clasp design
Answer: C: Insufficient contact of teeth and improper clasp design 
Explanation: None