If two angles are supplementary, what is their sum?

Two angles are defined as supplementary if the sum of their measures equals 180 degrees. This relationship is fundamental in geometry and is often used when discussing angle pairs in various contexts, such as the angles formed when two lines intersect. By understanding this definition, we see that the correct choice aligns perfectly with the established geometric principle that characterizes supplementary angles. Therefore, the sum of two supplementary angles is always 180 degrees.