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
The stiffness of the bristles of a nylon toothbrush is dependent on the: 
Select and explain. 
A. Diameter and length of filament, B. Amount of polish of filament, C. Colour of filament, D. Consistency of shape of the filament
A: Diameter and length of filament
Answer: A: Diameter and length of filament 
Explanation: None