Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

A chi-square test is most appropriate for tests concerning:
Option A:a single variance.
Option B:differences between two population means with variances assumed to be equal.
Option C:differences between two population means with variances assumed to not be equal.

Answer: A