If 2 angles are supplementary, then the angles a. add to 180 b. are congruent c. are vertical d. add to 90

Your answer would be A add to 180 degrees. The definition of a supplementary angle is when 2 non adjacent or adjacent angles add up.
They don't necessarily have to be congruent as 100 plus 80, or 50 plus 130 also add up to 180.
They aren't vertical angles since vertical angles are never adjacent.
They aren't complementary since only complementary angles add up to 90 degrees.
Hope it helps. Brainliest is always appreciated.