Final answer:
The sidelines are perpendicular by the Perpendicular Transversal Theorem.
Step-by-step explanation:
The correct answer is c. The sidelines are perpendicular by the Perpendicular Transversal Theorem.
The Perpendicular Transversal Theorem states that if a transversal intersects two parallel lines, then the alternate interior angles are congruent. In this case, the boldly marked lines labeled with the amount of yards are transversals intersecting the sidelines, which are believed to be parallel. Therefore, the lines must be perpendicular to each other based on this theorem.
For example, if we have two sidelines that are parallel to each other, and a transversal (the boldly marked line) intersects the sidelines, the alternate interior angles formed will be congruent. This confirms the perpendicular relationship between the sidelines.