You may recall that a square is a special case of rectangle, that is, one in which all the sides are equal (congruent). Additionally, a rectangle is a special case of a parallelogram, that is, one in which each angle is equal to 90° (a right angle). A parallelogram is a quadrilateral (four-sided polygon) with parallel and congruent opposite sides. A square meets these criteria 100 percent of the time, because all its sides are parallel and congruent, so choose always.