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': 'K flex file is made up of \nSelect and explain. \nA. Triangular blank, B. Rhomboid blank, C. Round blank, D. Rectangular blank', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]