Sing the textbook example of 420 california school districts and the regression of test scores on the student-teacher ratio, you find that the standard error on the slope coefficient is 0.51 when using the heteroskedasticity-robust formula, while it is 0.48 when employing the homoskedasticity-only formula. when calculating the t-statistic, the recommended procedure is to: a. first test for homoskedasticity of the errors and then make a decision. b. make a decision depending on how much different the estimate of the slope is under the two procedures. c. use the homoskedasticity-only formula because the t-statistic becomes larger. d. use the heteroskedasticity-robust formula.