What best describes a parallelogram?

• A. A closed two-sided figure.
• B. A closed four-sided figure in which the opposite sides are parallel.
• C. A circle with four sides.
• D. A polygon with six sides.

Answer: (B)

A parallelogram is a closed four‑sided polygon in which both pairs of opposite sides are parallel. That defining feature—opposite sides running parallel—is what sets it apart from other shapes and leads to properties like opposite sides being equal and diagonals bisecting each other. So the best description is a closed four‑sided figure with opposite sides parallel. The other descriptions don’t fit: a two‑sided figure isn’t a standard polygon; a circle with four sides isn’t a circle; a six‑sided polygon is a hexagon.