In Testing the Difference Between Two Population Means, Using Two $\bar { X } _ { 1 } - \bar { X } _ { 2 }$

Multiple Choice

In testing the difference between two population means, using two independent samples, the sampling distribution of the sample mean difference $\bar { X } _ { 1 } - \bar { X } _ { 2 }$ is normal if the:

A) sample sizes are both greater than 30.
B) populations are normal.
C) populations are non-normal and the sample sizes are large.
D) All of these choices are correct.