B all sides are the same length.
A square is a quadrilateral with all equal sides and is a plane figure with four right angles (90 degree angles). A square is a parallelogram. This means that all sides are parallel to each other and will never intersect. So, D can be right, but is not the best description of a square. A rectangle is also a parallelogram, so D's description isn't specific to squares. C is partially correct, but is wrong considering a square has 4 parallel sides. A is incorrect, it is the description of a rectangle. That is why the BEST description of the sides of a square is B, all sides are the same length.
I hope this helps:)
