To test whether or not the population regression function is linear rather than a polynomial of order r:.A) check whether the regression R2 for the polynomial regression is higher than that of the linear regression. B) compare the TSSfrom both regressions. C) look at the pattern of the coefficients: if they change from positive to negative to positive, etc., then the polynomial regression should be used. D) use the test of (r-1) restrictions using the F-statistic.