The correct summary is: A parallelogram has two lines of reflection that carry it onto itself: one horizontal through the midpoints of each side, and one vertical through the midpoints of the top and bottom.
This option accurately reflects the properties of a parallelogram regarding its lines of symmetry. A parallelogram has two lines of symmetry: one vertical line through the midpoints of opposite sides and one horizontal line through the midpoints of the other two sides. It is important to note that there are also lines of symmetry along the diagonals, typically considered in a square but not in the general case of a parallelogram. Therefore, if we're talking specifically about standard parallelograms (excluding squares), the mentioned option is the most correct.