Question

Which set of shapes contains members that are always similar to one another?.

Answer 1

Answer: Equilateral triangles.

Explanation: We know that in similar polygons, its all the corresponding angles are congruent. Only the set of equilateral triangles contains members that are always similar( by AAA similarity criteria) to one another as the measure of all the angles of equilateral triangle is fixed i.e. 60°.
Rest other do not have fixed measure for angles in it.