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

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: $\begin{array}{|l|l|}\hline A.&\text {sample sizes are both large. }\\\hline B.&\text {populations are normally distributed. }\\\hline C.&\text {populations have equal variances. }\\\hline D.&\text { populations are normal with equal variances.}\\\hline \end{array}$