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问题如下：

We often want to know whether a mean value differs for two groups. The samples are from populations at least approximately normally distributed and that the samples are also independent of each other. The test of the differences of means is using the assumption that the population variances are equal. Which type of test is used to test?

选项：

A.Paired comparisons t-test B.T-test using a pooled estimator of the common variance C.chi-Square test

解释：

When the test of the differences of means is using the assumption that the population variances are equal, in the calculation of the test statistic, we combine the observations from both samples to obtain a pooled estimate of the common population variance.