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
Recommended time for acid etching before placing a pit and fissure sealant 
Select and explain. 
A. 30 sec., B. 60 sec., C. 90 sec., D. 120 sec.
A: 30 sec.
Answer: A: 30 sec. 
Explanation: None