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': 'Most objective sign of gingivitis is \nSelect and explain. \nA. Increase in gingival size, B. Increase in crevicular fluid, C. Increase in gingival redness, D. Bleeding on probing', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]