In testing the difference between two population means for which the population variances are unknown and not assumed to be equal,two independent samples are drawn from the populations.Which of the following tests is appropriate?

A) z-test
B) pooled-variances t-test
C) unequal variances t-test
D) None of these choices.

When population variances are unknown and assumed to be unequal, the appropriate test to use is the unequal variances t-test. This test takes into account the possibility of the two populations having different variances, which can affect the calculation of the standard error and therefore the test statistic. The z-test is only appropriate when the population variances are known, while the pooled-variances t-test assumes that the population variances are equal. Thus, the correct choice is the unequal variances t-test (option C).