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': 'Retention grooves for class 3 restoration are placed: \nSelect and explain. \nA. Bucco axial and linguo axial line angles., B. Occlusoaxial line angles., C. Axiogingival line angle., D. Retention grooves are not possible in class 3 preparation.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]