An Individual Experiences Sadness and Melancholia in September Continuing Through

An individual experiences sadness and melancholia in September continuing through November. Which of the following factors should a nurse identify as most likely to contribute to the etiology of these symptoms?

A) Gender differences in social opportunities that occur with age
B) Drastic temperature and barometric pressure changes
C) A seasonal increase in social interactions
D) Variations in serotonergic functioning
E) Inaccessibility of resources for dealing with life stressors