References about this question: The t Test for Independent Means; The Distribution of Differences between Means; Estimating the Population Variance; Hypothesis Testing with a t Test for Independent Means; Assumptions of the t Test for Independent Means; Effect Size and Power for the t Test for Independent Means

Effect size is a major contribution to power. Another factor that, when increased, raises power is?

The sample's standard deviation

The sample's variance

The sample size

The mean of the sample