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
Age was found to be a factor affecting the relation of diabetes mellitus and periodontics 
Select and explain. 
A. Sampling Bias, B. Selection Bias, C. Confounding Bias, D. Information Bias
C: Confounding Bias
Answer: C: Confounding Bias 
Explanation: None