Please help me choose a topic for my I.O.P?

I'm doing it on the great gatsby, please help me! I honestly am stumped for an idea, I'm hopping anywhere from infidelity to karma to frauds, but I can't seem to think of a legit idea with backup. Please help me decide, I'm desperate to find a topic for my presentation. Oh and for those of you who don't know what I.O.P is it's an international oral presentation, i think at least.