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
In modified class III cavity restoration retention is obtained mainly by 
Select and explain. 
A. Acid etching, B. Retentive groove/slot, C. Retentive point, D. Retentive pin
A: Acid etching
Answer: A: Acid etching 
Explanation: None