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': 'Bone graft procedures are most successful in treating: \nSelect and explain. \nA. In furcation involvements, B. Deep, two-wall craters, C. Narrow three-wall defects, D. Osseous defects with one remaining wall', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]