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 CPITN probe has a ball end of which diameter & marking at what level: 
Select and explain. 
A. 0.5 mm diameter ball and marking at 3,5,8 and 11.5 mm., B. 1.0 mm diameter ball and marking at 3.5, 5.5, 8.5 and 11.5 mm., C. 0.5 mm diameter ball and marking at 3.5, 5.5, 8.5 and 11.5 mm., D. 1.0 mm diameter ball and marking at 3,5,8 and 11.5 mm.
C: 0.5 mm diameter ball and marking at 3.5, 5.5, 8.5 and 11.5 mm.
Answer: C: 0.5 mm diameter ball and marking at 3.5, 5.5, 8.5 and 11.5 mm. 
Explanation: None