Theories that focus on the aesthetic relationship between parts within a work are known as theories.
a. expressive
b. formal
c. rhetorical
d. mimetic

Theories that focus on the aesthetic relationship between parts within a work are known as "formal" theories.

Formalism in aesthetics has customarily been taken to allude to the view in the theory of craftsmanship that the properties in prudence of which a work of art is a fine art—and in excellence of which its esteem is resolved—are formal in the feeling of being open by coordinate sensation (normally sight or hearing) alone.Yet in the mid twenty-first century there has been a recharged enthusiasm for and barrier of Formalism.

it is the last choice