What is meant by confounding?
A. Confounding in a study occurs when a single explanatory variable has a great effect on a response variable. This sometimes causes a misleading interpretation of the relationship between the two variables.
B. Confounding in a study occurs when there is little or no actual relationship between the explanatory and response variable other than random chance. This sometimes causes completely unrelated variables to appear to have a causal relationship, and can cause variables that have almost no relationship to have a very strong relationship.
C. Confounding in a study occurs when the effects of two or more explanatory variables are not separated. Therefore, any relation that may exist between an explanatory variable and the response variable may be due to some other variable or variables not accounted for in the study.
D. Confounding in a study occurs when the effects of the explanatory variable are caused, in some part, by the effects of the response variable. When there is zero confounding in a study, the effects of the response variable are entirely caused by the effects of the explanatory variable.

In a study, if we want to measure of establish a relation between two variables, we say that there is a confounding variable when there is a third variable that is having an effect on our original two variables but this third variable wasn't originally measured in our study. Therefore our results are misleading because the relation between our two variables is being influenced by the confounding one.

This is why the correct answer would be the a) An explanatory variable has a great effect on a response variable. And this causes a misleading interpretation between the two variables.