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
Acid-etching is done for 
Select and explain. 
A. 30 Seconds, B. 60 seconds, C. 90 seconds, D. 120 seconds
A: 30 Seconds
Answer: A: 30 Seconds 
Explanation: None