Which element in a story can help the reader better understand the storys theme ?

One of the most important things are the morals in the story, if a person has the ability to read between the lines and can connect the storyline with the morals then the theme becomes crystal clear

b. failure at least that one seems the most negative out of all of the answers provided pls correct me if i'm wrong. : ))

i think the answer is invented words, rhyming knack, alliteration, and, metaphor.