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': 'Activity index of GCF shows ? \nSelect and explain. \nA. IL-B/IL-RC, B. IL-RC/IL-B, C. RANK / OPG, D. OPG/ RANK', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]