Most people feel lonely sometimes, but it usually only lasts a few minutes or a few hours. This kind of loneliness is not serious. In fact, it is quite normal. For some people, though, loneliness can last for years. Now researchers say there are three different types of loneliness. The first kind of loneliness is temporary. This is the most common type. It usually disappears quickly and does not require any special attention. The second kind, situational loneliness, is a natural result of a particular situation-for example, the death of a loved one, or moving to a new place. Although this kind of loneliness can cause physical problems, such as headaches and sleeplessness, it usually does not last for more than a year. Situational loneliness Is easy to understand and to predict. The third kind of loneliness is the most severe. Unlike the second type, loneliness usually lasts more than two years and has no specific cause. People who experience habitual loneliness have problem socializing and becoming close to others unfortunately, many chronically lonely people think there is little or nothing they can do to improve their condition. Many researchers agree that the loneliest people are between the ages 18 and 25, so a group of psychologists decided to study a group of college students. They found that more than 50% of the students were situationally lonely at the beginning of the term as a result of their new circumstances, but had adjusted after a few months, 13% were still lonely after seven months due to shyness and fear. They felt very uncomfortable meeting strangers, even though they understood that their fear was not reasonable. The situationally lonely students overcame their loneliness by making new friends, but the chronically lonely remained unhappy because they were afraid to do so. Psychologists are trying to find ways to help habitually lonely people for two reasons: First of all, they are unhappy and unable to socialize and there is a connection between chronic loneliness and serious illness such as heart disease. While temporary and situational loneliness can be a normal, healthy part of life, chronic loneliness can be a very sad, and sometimes dangerous condition. The passage mainly talks about    _    .
the subjects of psychology the study on loneliness the interests of psychologists the treatment of loneliness