In the "before and after" specification with n=1,500 individuals and 3 regressors: the "entity-demeaned" estimator will provide the same estimate of the slope coefficients as the first difference estimator. Oa. Ob. including 1,499 individual effects as binary variables will provide the same slope coefficients estimate as the "entity-demeaned" estimator. Oc. including 1,499 individual effects as binary variables will provide the same slope coefficients estimate as the first difference estimator. Od.including 1 dummy variable for the second time period and 1,499 individual effects as binary variables will provide the same slope coefficients estimates as the first difference estimator. Oe. All of the above. Of. None of the above