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': 'Protapers of same tip diameter are \nSelect and explain. \nA. Sx-S1, B. S1-S2, C. S2-F1, D. Sx-S2', 'role': 'user'}, {'content': 'Answer: C \nExplanation: PROTAPER INSTRUMERNTS\n\nA unique feature of Pro Taper instructions is each one has changing percentage tapers over the length of the cutting blades.\nPro taper instruments have convex, triangular cross – sections, a changing helical angle and push over their cutting blades and a non-cutting, modified guiding tip.\nThe Pro Taper system is comprised of three Shaping and three Finishing instruments.', 'role': 'assistant'}]