Final answer:
Alice and John's disagreement about their relationship is the event from 'Fourteen' that pertains to the falling action of the plot, as it signifies the decrease of tension post-climax and moves towards the story's resolution.
Step-by-step explanation:
The event from Alice Gerstenberg's "Fourteen" that belongs to the falling action stage of the plot structure is (d) Alice and John have a disagreement about their relationship. In the context of plot structure, the falling action follows the climax of a story, where the tension and conflicts begin to be resolved and lead towards the resolution or dénouement. Since the falling action involves winding down the events post-climax and showing the outcomes of the characters' decisions or changes, a disagreement between Alice and John suggests a release of tension and a move towards resolving their story arc.