1. The problem asks which theorem(s) explain why a rectangle is a parallelogram. 2. A rectangle is a quadrilateral with four right angles, meaning each angle measures 90 degrees. 3. To prove a rectangle is a parallelogram, we need to use theorems that define parallelograms based on angle or side properties. 4. The relevant theorem is: "If an angle of a quadrilateral is supplementary to both its consecutive angles, then the quadrilateral is a parallelogram." 5. Since each angle in a rectangle is 90 degrees, and 90 + 90 = 180 degrees, each angle is supplementary to its consecutive angles. 6. Therefore, by this theorem, the rectangle is a parallelogram. 7. Other theorems listed do not directly apply based on the given information about angles alone. Final answer: The correct theorem is option B.