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 is an over the counter bleaching agents: 
Select and explain. 
A. Sodium perborate., B. Hydrogen peroxide., C. Carbamide peroxide., D. None.
C: Carbamide peroxide.
Answer: C: Carbamide peroxide. 
Explanation: None