Two Independent Samples of Sizes 30 and 40 Are Randomly $\bar { X } _ { 1 } - \bar { X } _ { 2 }$

Multiple Choice

Two independent samples of sizes 30 and 40 are randomly selected from two populations to test the difference between the population means, µ?1 - µ?2, where the population variances are unknown but equal. 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.