A researcher's regression results are shown below using n = 8 observations. Variable Coefficients Standard Error Intercept -0. 1667 2.8912 X1 1.8333 0.2307 Which is the 90 percent confidence interval for the slope? Note that to.05 to.025 to.01 df=7 1.895 2.365 2.998 df=6 1.943 2.447 3.143 df=5 2.015 2.571 3.365 O a. [1.118, 2.449] O b. [1.268, 2.398] O c. [1.602, 2.064] O d. [1.333, 2.284] O e. [1.385, 2.282]