Passage 4
Questions 16 to 20 are based on the following passage.
Some estimates are that as many as 8% of adolescents suffer from depression at some time during any one-year period, making it much more common than, for example, eating disorders, which seem to get more attention as a source of adolescent misery.
Even among psychiatrists and other mental health care professionals, the extent of the disability caused by depression is vastly underestimated. The World Health Organization has found that major depression is the single greatest cause of disability in the world—more than twice as many people are disabled by depression as by the second leading cause of disability，iron-deficiency anemia (贫血症).Other diseases and disorders may get more press coverage or more research money, or more sympathy and concern from a well-meaning public, but major depression causes more long term human misery than any other single disease.
When I was a resident in psychiatry，we believed that true depression was rare among teenagers, or that insofar as it existed, it was just a normal phase of adolescent development with no lasting consequences. It didn’t take long after I began treating troubled kids to see that this couldn't possibly be true. Research over recent decades has confirmed my impression. These beliefs, if any still holds them, are false and dangerous. In fact, early onset of depression is not normal, and can predict numerous unhappy life events for youngsters, including school failure, teenage pregnancy, and suicide attempts.Although depression is increasingly common today, it is among the oldest diseases recorded in the history of medicine. As early as the fourth century, the symptoms of “melancholia” were well known. In other words，depression was first thought of as an exclusively physical illness-the loss of appetite， sleeplessness，irritability，and general depression was believed to have a physical，not a psychological cause. It wasn’t until the nineteenth century-when the term depression was invented to substitute for melancholia-that a psychological understanding of the illness began to develop. Eventually this psychological explanation of depression would become the only one, although today it no longer is. We now know that depression has both psychological and physical symptoms, and that both psychological and medical treatments can help to alleviate them.
In the 4th century, depression was regarded as a_____.