Seasonal Affective Disorder (SAD) is a type of depression that's related to changes in seasons. It typically begins and ends at about the same times every year. For most people with SAD, symptoms start in the fall and continue into the winter months, sapping energy and making them feel moody. Less commonly, SAD causes depression in the spring or early summer. Treatment for SAD can include light therapy, medication, and psychotherapy.
Which of the following pieces of information is MOST relevant to understanding the *causes* or *triggers* of Seasonal Affective Disorder, according to the text?
A) The effectiveness of psychotherapy in treating SAD.
B) The specific chemical pathways involved in light therapy.
C) The seasonal changes that affect its onset and duration.
D) The historical prevalence of SAD in different cultures.
E) The economic impact of SAD on productivity.