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': 'Possible contra indications for periapical surgery are \nSelect and explain. \nA. Controlled diabetis mellitus, B. The danger of damage to adjacent structures, C. A history of rheumatic fever, D. Congenital heart disease', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]