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
Which of the following alloys has the highest surface roughness? 
Select and explain. 
A. Stainless steel, B. Elgiloy, C. NiTi, D. TMA
C: NiTi
Answer: C: NiTi 
Explanation: The surface of NiTi is rougher (because of surface defects, not the quality of polishing) than that of beta-Ti, which in turn is rougher than steel.
However, there is little or no correlation for orthodontic wires between the coefficients of friction and surface roughness. (i.e., interlocking and plowing are not significant components of the total frictional resistance).

Ref: Profitt 4th edition page 378