What is the sum of the measures of supplementary angles?

Supplementary angles are defined as two angles whose measures add up to 180 degrees. This definition is central to understanding the concept of supplementary angles in geometry. For example, if one angle measures 120 degrees, its supplementary angle would measure 60 degrees, as 120 + 60 = 180 degrees.

Therefore, when presented with a question regarding the sum of the measures of supplementary angles, the correct answer reflects this fundamental property of supplementary angles, which is 180 degrees. The other options represent different sums that pertain to other geometric relationships but do not apply in this context of supplementary angles.