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
[{'content': 'In modified class III cavity restoration retention is obtained mainly by \nSelect and explain. \nA. Acid etching, B. Retentive groove/slot, C. Retentive point, D. Retentive pin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]