Mason Turner has had "mood swings" for about the past five years. His "high" periods are relatively short-lived and are characterized by an increase in goal-directed activity and an inflated sense of self-esteem. When Mason experiences "low" periods, they, too, are of short duration and characterized by a depressed mood and subsequent fatigue.
While Mason does not consider his present problems severe, his wife, Yvonne, feels that he might need some help. Given these symptoms, Mason is most likely suffering from which mood disorder?

a) Double depression
b) Persistent depressive disorder (dysthymia)
c) Bipolar I disorder
d) Cyclothymic disorder