Carleen Comes to Therapy Because She Is Feeling Sad

Carleen comes to therapy because she is feeling sad. Carleen says she has often had periods of extreme sadness in the past and they typically last between 6 and 8 months. During those times she overeats, has trouble sleeping, feels exhausted all the time, and thinks a lot about dying. At other times, however, Carleen says she feels wonderful. During those times, which last about a week, she gets a lot done, feels as if she could do anything, talks a lot and quickly, and doesn't sleep but doesn't feel tired. Carleen says her "up" times are great and have never caused her any trouble. Carleen's most likely diagnosis is ________

A) major depressive disorder.
B) persistent depressive disorder.
C) bipolar I.
D) bipolar II.