The sentence that shows proper parallel structure is B) Judith dislikes people who are rude, selfish, and self-centered.
It is called parallel structure to the repetition of a grammatical form within the same sentence. In other words, it refers to the use of the same grammatical pattern in order to make the sentence clearer for the reader.
In sentence B) "people" is modified by a defining relative clause ("who are rude, selfish and self-centered"). The defining relative clause includes three adjectives ("rude", "selfish" and "self-centered") and that is what makes the sentence a parallel structure.
Sentence B) is the only sentence where grammatical forms have not been mixed. Sentence A) presents two independent clauses ("Judith dislikes people who are rude, selfish" and "they are self-centered"), which results in the separation of the last adjective and a breakdown in the parallel construction. In sentence C) "self-centered" is premodified by the adverb "very", which also creates a faulty parallelism. Sentence D) does not show a proper parallel structure either since it includes a verb ("act") in the defining relative clause.