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, we use the pooled variance in estimating the standard error of the sampling distribution of the sample mean difference $\bar { X } _ { 1 } - \bar { X } _ { 2 }$ if the:

A) sample sizes are both large.
B) populations are normally distributed.
C) populations have equal variances.
D) populations are normal with equal variances.