Option E refers to a polygon with only one set of parallel sides, which describes a trapezoid, not a parallelogram.
The question which asks to identify polygons with at least one set of parallel sides but is not a parallelogram falls under the category of Mathematics, specifically in geometry. When we discuss shapes in geometry, a parallelogram is a special type of polygon with two pairs of parallel sides. For a shape to not be a parallelogram but still have a set of parallel sides, it could be a trapezoid or a triangle with a pair of parallel sides but not two pairs.
Specifically, Option E refers to a polygon that has only two parallel sides. This description fits a trapezoid, which by definition has only one pair of parallel sides unlike parallelograms which must have two. This exclusion makes the trapezoid the correct answer to the given problem.