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
Periodontal endoscopes work on the principle of: 
Select and explain. 
A. Fiberoptics, B. Magnetorestrictive, C. Piezoelectric, D. All of the above
A: Fiberoptics
Answer: A: Fiberoptics 
Explanation: None