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': 'Undersurface of pontic should be \nSelect and explain. \nA. Concave mesio distally and convex buccolingually, B. Convex mesio distally and concave buccolingually, C. Convex in all directions, D. Concave in all directions', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]