The statement that best describes how the author uses conflict to convey a theme in this story is:
by revealing Gortsby's disgust and cynicism toward his own actions in life.
This is because the setting reflects Gortsby's inner feelings and the theme of defeat and lost hopes, particularly as he observes the people around him and considers their struggles as well as his own. The conflict is largely internal, focused on Gortsby's perceptions and judgments of those he sees, including himself.