Confounding Factor is:: (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.
Answer is D. 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