Final answer:
In the t test for independent groups, the unbiased estimate of the population variance is S2 squared alone.
Step-by-step explanation:
In the t test for independent groups, the unbiased estimate of the population variance is (b) S2 squared alone.
When conducting a t test for independent groups, the population standard deviations and variances are usually unknown. In this case, the unbiased estimate of the population variance is calculated using only the sample variance of the second group, denoted as S2 squared.