In Which of the Following Tests Is the Variable of Interest

Multiple Choice

In which of the following tests is the variable of interest the difference between the values of the observations from the two samples,rather than the actual observations themselves?

A) A test of hypothesis about the mean of a population of paired differences selected from two related samples.
B) A test of hypothesis about the difference between the means of two normally distributed populations using independent samples.
C) A test of hypothesis about the difference between two population proportions,using large independent random samples.
D) A test of hypothesis about the difference between the variances of two normally distributed populations using independent samples.