The theme of the story is the moral or the lesson. When reading the story, what lesson is portrayed the most throughout the passage? Also, the theme can be applied to everyone. In other words, it is universal. For example, in Finding Nemo, one could say that the theme is family will always be there to help when needed. Which of the answers given here would work best for the passage you are reading?
Extraneous means irrelevant or unneeded. essential means absolutely needed. so they are opposites. The other opposites in that set are mediocre (meh average) and extraordinary(amazing) D