a. What is a residual? b. In what sense is the regression line the straight line that "best" fits the points in a scatterplot? a. What is a residual? A. A residual is a value of y-y, which is the difference between an observed value of y and a predicted value of y. OB. A residual is a value that is determined exactly, without any error. OC. A residual is a point that has a strong effect on the regression equation. OD. A residual is the amount that one variable changes when the other variable changes by exactly one unit. b. In what sense is the regression line the straight line that "best" fits the points in a scatterplot? The regression line has the property that the of the residuals is the possible sum.