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
Retention in a composite restoration is mainly attained by 
Select and explain. 
A. Chemical adhesion, B. Acid etching & Bonding, C. Inverted Truncated shape, D. Undercuts
B: Acid etching & Bonding
Answer: B: Acid etching & Bonding 
Explanation: None