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
Glucose levels in gingival crevicular fluid (GCF) are: 
Select and explain. 
A. Equal to glucose level in serum, B. Zero, C. 3-4 times greater than serum levels, D. More than 10 times the serum Levels
C: 3-4 times greater than serum levels
Answer: C: 3-4 times greater than serum levels 
Explanation: None