Question 20 of 20 : Select the best answer for the question. 20. Testing the difference between two population means using two independent samples, the sampling distribution of the sample mean difference x1 x2 is normal if the O A. populations are normal. 0 B. populations are at least normally distributed with equal variances. O C. sizes are both greater than 30. O D. populations are nonnormal with unequal variances. Question 19 of 20 : Select the besl' answer for the question. 19. In order to conduct a formal statistical test of the hypothesis this entails numerical measures of the difference between the treatment means and the sampling variability within each of the treatments. The variation between the treatment means is measured by the O A. Mean Square for Treatments (MST). O B. Mean Square for Error (MSE). O C. Sum of Squares for Errors (SSE). O D. Sum of Squares for Treatments (SST)