Marcus has really enjoyed high school. He is working hard to get his grades up. Some days he feels like he is doing it all, getting so much done, and can pile on more. Then he will have a few days where he is totally overwhelmed, withdrawn, and can barely manage schoolwork. That puts him behind, and he has to work twice as hard when he feels better. His parents are worried about his mental health. What mental illness might he be experiencing? A. Stress B. Depression C. Schizophrenia D. Bipolar disorder.