Final answer:
The Same-Side Interior Angles Theorem is a mathematical concept in geometry dealing with the supplemenatry angles formed when parallel lines are intersected by a transversal.
Step-by-step explanation:
The correct answer is C) A mathematical concept. The Same-Side Interior Angles Theorem (SSIA Theorem) pertains to geometry, a branch of mathematics that deals with points, lines, shapes, and figures. This theorem is specifically concerned with the angles formed when two parallel lines are cut by a transversal. According to the SSIA Theorem, same-side interior angles are supplementary, meaning that their measures add up to 180 degrees. This theorem helps students understand the relationships between angles and can be used to solve problems involving parallel lines and transversals.