Stress is with us all the time. It comes from mental or emotional activity as well as physical activity. It is unique and personal to each of us. So personal, in fact, that what may be relaxing to one person may be stressful to another. For example, if you’’re a busy executive who likes to keep occupied all of the time, "taking it easy" at the beach on a beautiful day may be extremely frustrating, nonproductive, and upsetting. You may be emotionally distressed from "doing nothing." Too much emotional stress can cause physical illnesses such as high blood pressure, ulcers, or even heart disease. Physical stress from work or exercise is not likely to cause such ailments. The truth is that physical exercise can help you to relax and to better handle your mental or emotional stress.
A source of stress NOT specifically mentioned in this passage is________.
A．educational activity
B．physical activity
C．mental activity
D．emotional activity