On a plot structure diagram, the climax is C. the turning point of the story.
The climax is usually where there is a major change in the plot of the story and it either benefits or does not benefit the main character(s). This is where you can kind of predict what the outcome of the story will be.
The answer is not A. because another word for the beginning would most likely be exposition, where the characters and setting are just getting introduced.
The answer cannot be B. because the location of the story is always going to be setting.
The answer also is not D. because an event following the resolution is too far away from the climax-- this is usually somewhere around the middle/end but before the other plots.