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
The laser useful in smear layer removal is 
Select and explain. 
A. Er:Cr:YSGG, B. Er:YAG, C. Ne:YAG, D. Argon Laser
A: Er:Cr:YSGG
Answer: A: Er:Cr:YSGG 
Explanation: Erbium: Chromium: Yttrium Scandium Gallium Garnet Laser (Er:Cr:YSGG)

Etches enamel surface.
Removal smear layer.

 Erbium: Yttrium Aluminium Garnet Laser (Er:YAG)

Remove caries in enamel and dentin.
Removes dislodged GIC and Composite. 
Desensitize the hypersensitivity dentin.

 Neodymium - Yttrium Aluminum Garnet Laser (Ne: YAG)  

Good hemostasis.
Used in non-surgical sulcular debridement.

 Argon Laser 

Yield high intensity visible blue light. 
Curing of dental restorations.
It also changes the surface chemistry of both enamel and root surfaces dentin, which reduces the probability of recurrent caries. 
Removes extrinsic and intrinsic stains.
Bleaching of teeth.