What type of variable does a t-test typically compare?

A t-test is specifically used to compare the means of continuous quantitative variables between two distinct groups. The essence of a t-test lies in assessing whether there is a statistically significant difference in the means of these two groups based on sample data.

When considering the other types of variables listed, qualitative and categorical variables involve classifications rather than measurements on a numerical scale, which is not suitable for a t-test that relies on mean comparisons. The term "multiple categorical groups" refers to scenarios suited for other statistical tests like ANOVA, which is designed to compare means across three or more groups rather than just two. Therefore, the focus on continuous variables allows the t-test to effectively explore the differences in a measurable way, making option C the accurate response.