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
Which of the following drugs is most frequently used in treating refractory periodontitis, including localized juvenile periodontitis? 
Select and explain. 
A. Metronidazole and Amoxicillin, B. Tetracycline, C. Ciprofloxacin, D. Penicillin
A: Metronidazole and Amoxicillin
Answer: A: Metronidazole and Amoxicillin 
Explanation: None