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
Confounding Factor is: 
Select and explain. 
A. Itself a risk factor for the disease., B. Associated with both exposure and disease., C. Is distributed unequally in study and control group., D. All of the above.
D: All of the above.
Answer: D: All of the above. 
Explanation: Confounding factor:

One which is associated with BOTH exposure and disease and is distributed UNEQUALLY in study and control group.
It is itself a RISK FACTOR for the disease. 
e.g. – study of coffee drinking and lung cancer – if coffee drinker is also a cigarette smoker then this cigarette smoking is a confounding factor. Confounding factor can be neutralized by MATCHING