Consider the characteristics of a "confounding variable." Which one or more of these fully describe the minimal characteristics that must be met for a variable to be a confounding variable. a. It is not associated with the explanatory variable or the response variable. b. It is not associated with the explanatory variable and it is associated with the response variable. c. It is associated with the explanatory variable and is not associated with the response variable. d. It is associated with the explanatory variable and with the response variable.