In What Type of Test Is the Variable of Interest

Multiple Choice

In what type of test is the variable of interest the difference between the values of the observations rather than the observations themselves?

A) a test of the equality of variances from 2 independent populations
B) a test of the difference between the means of 2 related populations
C) a test of the difference between the means of 2 independent populations
D) a test for of equality of variances from two related populations.