Which one of the following latitudes forms a great circle?

A great circle is the largest possible circle that can be drawn on a sphere and divides the sphere into two equal halves. The equator (0° latitude) is a great circle because it passes through Earth's center and divides the Earth into northern and southern hemispheres. All other latitudes (like 23.5° or 66.5°) are small circles - they don't pass through Earth's center. Longitudinal lines (meridians) are also great circles, but they weren't options.