Which explains whether or not a parallelogram can be classified as a rectangle? A parallelogram is also a rectangle. Both quadrilaterals have four right angles. A parallelogram is also a rectangle. Both quadrilaterals have opposite sides that are congruent, opposite sides that are parallel, and four congruent angles. A parallelogram is not a rectangle. A rectangle has opposite sides that are congruent, and a parallelogram does not. A parallelogram is not a rectangle. A rectangle must have four right angles, and a parallelogram must only have opposite angles congruent.