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
Most objective sign of gingivitis is 
Select and explain. 
A. Increase in gingival size, B. Increase in crevicular fluid, C. Increase in gingival redness, D. Bleeding on probing
D: Bleeding on probing
Answer: D: Bleeding on probing 
Explanation: None