My answer: all of the above are correct.
- A quadrilateral is a figure with 4 sides. Both a parallelogram and a square have 4 sides exactly.
- Opposite sides of a square and parallelogram are equal. This is proved on a square as all the sides are 90 degrees. For a parallelogram, proof that its sides are parallel, is that each pair of sides are all of equal length.
- A trapezoid does have only 1 pair of parallel lines. It is a figure that has one pair of parallel lines of equal length, and 2 other sides with unequal length.