An analyst is comparing the annual mean returns for the past 40 years on the S&P 500 index to the annual mean returns on the NYSE Composite index for the same period. The analyst believes that the indices are highly similar and wants to test her hypothesis that the difference in the annual returns is not significantthe difference in returns is really zero. The analyst assumes that the population variances are equal. The type of test that the analyst most likely will use is a:

Group of answer choices

a. paired comparison test because the two samples are dependent.

b. mean difference test because the two population variances are assumed to be equal.

c. paired comparison test because the two population variances are assumed to be equal.