Answer: Square.
Explanation:
First it is important to know the following definitions:
1. A Quadrilateral is defined as a polygon that has four sides and, therefore, four vertices.
2. A Square is a Regular Quadrilateral that has the following properties:
- All its sides have equal length.
- Its opposite sides are parallel.
- The measure of each Internal angle is 90 degrees (which are also called "Right angles").
According to the information given in the exercise, the poster Cecily made has the shape of a Quadrilateral. All the angles of this quadrilateral are congruent (this means that they have equal measure) and all the sides are also congruent (they have the same length).
Therefore, based on the explained before, you can conclude that it is a Square.