Two Independent Samples of Sizes 50 and 50 Are Randomly $\mu _ { 1 } - \mu _ { 2 }$

Two independent samples of sizes 50 and 50 are randomly selected from two populations to test the difference between the population means, $\mu _ { 1 } - \mu _ { 2 }$ . The sampling distribution of the sample mean difference $\bar { x } _ { 1 } - \bar { x } _ { 2 }$ is:

A) normally distributed.
B) approximately normal.
C) t-distributed with 98 degrees of freedom.
D) chi-squared distributed with 99 degrees of freedom.