Two Independent Samples of Sizes 30 and 40 Are Randomly $\mu$

Two independent samples of sizes 30 and 40 are randomly selected from two populations to test the difference between the population means, µ $\mu$ ₂ - µ $\mu$ _1, where the population variances are unknown. Which of the following best describes the sampling distribution of the sample mean difference $\bar { x } _ { 1 } - \bar { x } _ { 2 }$ ?

A) Normal.
B) t-distributed with 68 degrees of freedom.
C) Approximately normal.
D) None of these choices are correct.