In Testing the Difference Between the Means of Two Normally $\bar { x } _ { 1 } - \bar { x } _ { 2 }$

In testing the difference between the means of two normally distributed populations using independent random samples with known variances,the distribution of the difference in sample means $\bar { x } _ { 1 } - \bar { x } _ { 2 }$
Will be normally distributed under which of the following conditions?

A) Equal sample sizes.
B) Both population standard deviations are known.
C) No other conditions are required.
D) Both sample sizes are very large.
E) Both population variances are equal.