Which statement is true about regular polygons?

In the context of regular polygons, the defining characteristic is that they are both equiangular and equilateral. This means that all sides are of equal length and all interior angles are of equal measure. Therefore, any regular polygon has an equal number of sides and vertices, as each vertex corresponds to a corner of the polygon where two sides meet.

Choosing the statement that regular polygons always have an equal number of sides and vertices accurately captures this fundamental property, making it the correct answer. Other options indicate misunderstandings of the definitions. Regular polygons cannot have an unequal number of sides and vertices, cannot be limited to just triangles and quadrilaterals, and cannot have varying side lengths as that would contradict the definition of being regular.