If parallel lines are cut by a transversal, then Select Choice supplementary.

When a transversal crosses parallel lines, it creates a variety of angles. The pairs of interior angles on the same side of the transversal are called consecutive interior angles, and they are supplementary, meaning their measures add up to 180 degrees. This property is crucial in geometry and is often used in proofs and problem-solving. In real-world applications, understanding the angles formed by parallel lines and a transversal can be essential in fields like architecture and engineering. For instance, when designing roads, the angle at which they intersect can affect traffic flow and safety, demonstrating that geometry is not just a theoretical subject but also a vital component of daily life and physical projects!