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 \nSelect and explain. \nA. Made of triangular blank, B. Made of square blank, C. Made of rhomboid blank, D. Made of round wires', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]