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 ideal occlusion, facial cusps of maxillary posterior teeth oppose \nSelect and explain. \nA. Grooves and embrasures, B. Grooves only, C. Marginal ridges and embrasures, D. Marginal ridges only', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]