Which of the following disorders is the most likely cause of this patient's symptoms?

A 16-year-old boy is brought to the office because he has had decreasing performance in school over the past six months. During this time, the patient has become more irritable and irresponsible, has changed his group of friends, and has had decreasing personal hygiene. He was previously a high-achieving student, but his grades have slipped to the extent that he is failing several courses. Which of the following disorders is the most likely cause of this patient's symptoms? (A) Bipolar (B) Conduct (C) Major depressive (D) Persistent depressive (dysthymic)