Which sentence is written in a formal writing style?
i really love my journalism class because it's super fun and engaging.
i know the local newspaper reporters don't have writing skills as good as me.
by taking journalism courses, one may be prepared for several exciting careers.
you know, working for a web design company is a really awesome thing to do.

The third sentence down is the right answer. It doesn't use slang.

By taking journalism courses, one may be prepared for several exciting careers. This is the correct option. The structure is complex. The sentence does not follow the canonical order or the expected order of Subject , verb and adverbial. The sentence begins with an adverbial: " By taking" and then, subject and predictate : " one (subject) may be prepared..". This non-canonical order is used in writing. The canonical or expected order would be: One may be prepared for several exciting careers by taking journalism courses. The vocabulary is formal : " journalism courses"; " one may be..."; " ..exciting.."

These statements are not correct:

-I really love my journalism class because it's super fun and engaging. The underlined words are used in colloquial  style and mainly this is oral. These expressions are informal.

-I know the local newspaper reporters don't have writing skills as good as me.   "Don't" is used in informal register. The formal equivalent is the full form: " do not..". "Me" is not correct; the word " mine" should replace it.

-You know, working for a web design company is a really awesome thing to do. The underlined words are used in colloquial  style and mainly this  is oral. These expressions are very informal.

this answer to this question is c. allegory

why?

stories with allegories have a hidden symbolic meaning with a theme. the hidden meaning can be political, or other real life problems.

what is the question?