Choose the word which is different from the rest.

The answer is C. Circle.

A triangle, rectangle, and square are all polygons, which are two-dimensional shapes with straight sides. A circle is a curved shape.

A triangle has three sides and three angles. A rectangle has four sides and four angles, with opposite sides parallel and opposite angles congruent. A square has four sides of equal length and four angles of equal measure, all of which are 90 degrees. A circle has no sides or angles.

The circle is the only shape that is not a polygon.