What can we learn from R, the coefficient of determination? A. R refers to whether the estimated cost function makes economic sense. B. R2 tests whether the slope of a regression line differs significantly from 0. C. R is a goodness-of-fit test. It tells us the percentage of variation in cost that is associated with changes in the cost driver. D. R is the hypothesis that a data set in a regression analysis follows the simpler of two proposed linear models that are nested within each other.