Definitely A. B, C, and D have nothing to do with finding the main idea
In this story, illness -specifically mental illness- is seen as temporary, and is not taken seriously. This is seen at the very beginning of the story, when the narrator indicates that her husband (a doctor) does not believe that she is truly ill. When a person is experiencing mental illness in this story, they are also believed to be cured by rest, exercise, and fresh air. Rather than today's methods of therapy and/or medication, the story describes merely taking a break from work and going away until one seems to be better.
