What is the most common purpose for composition in art?
a. it the artist create a meaningful experience.
b. it provides guidelines for artists, so that their pieces can be understood by the public.
c. it provides an understanding of, and agreement among, all the elements.
d. it ensures a realistic, proportional reproduction of a piece of art.

The most common purpose for composition in art is that it provides an understanding of, and agreement among, all the elements.  Correct C

The term composition denotes the arrangement of the visual elements in a painting or other artwork  in a way that is pleasing to the artist and, one hopes, the viewer. Composition defines if the art will be eye-catching or not. Elements of composition include: balance, movement, unity, rhythm, focus, contrast, proportion and pattern.