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
Most efficient removal of hard tissue is done by 
Select and explain. 
A. Er laser, B. Argon visible laser, C. Nd:YAG, D. HO: YAG
A: Er laser
Answer: A: Er laser 
Explanation: None