What Type of Test for Population Means Should Be Performed

Multiple Choice

What type of test for population means should be performed when examining a situation in which employees are first tested,then trained,and finally retested?

A) A z test under independent sampling with known population variances.
B) A t test under independent sampling with unknown but equal population variances.
C) A t test under dependent sampling.
D) A t test under independent sampling with unknown and unequal population variances.