For many years, officials of the National Institutes of Health have told Americans that they need to get enough sleep. They say this is necessary for people to stay healthy and do well. Now health officials begin to urge children to get enough sleep. They say children need at least nine hours of sleep every night. They say research shows that children who get this much sleep perform better in school and are less likely to become too fat.

Studies show that lack of sleep causes tiredness and problems with clear thinking. People who do not get enough sleep become angry easily. They also have trouble controlling their emotions.

Among children, problems that result from lack of sleep often are mistaken for more serious disorders. Unlike adults, tired children seem to have endless energy. Some doctors mistakenly identify this as hyper-activity. Many sleep disorders first develop in childhood. But doctors often do not identify the disorder until years later.

Experts say many American teenagers are not getting enough sleep. Teenagers stay up late for several reasons. For example, schoolwork, after school activities and late-night fun. Four years ago, education officials in Minneapolis changed the starting time of seven high schools. The officials delayed the starting time by almost ninety minutes.

A University of Minnesota study found that participation at the high schools improved after the starting time was changed. However, the later start did not greatly affect the performance of the students. Still, school systems in other parts of the country are discussing later starting times for high school students.

This summer, for the first time, Emory College let freshmen pick their own roommates in an online roommate-selection system. Students, using screen names to hide their identities, posted profiles of themselves detailing personality attributes, work habits, music and food preferences, and exchanged information using e-mail.

Housing officials at Emory say they expect that letting students pick their own roommates who are their closest matches will increase the likelihood of compatibility. And there’s little risk of hurt feelings if the e-mail exchanges do not lead to a match, since the initial round of contacts is done under screen names.

Several studies have shown that roommates have an impact on the attitudes and social behavior of those they live with. And one recent study found that a roommate’s academic performance has a small, but statistically significant, effect on the other roommate’s grade-point average. Other studies, however, did not find that effect.

The business of assigning roommates varies widely across the country. At Davidson College, the housing staff sort every freshman with careful hand-selection. The Davidson philosophy is that roommates should be as similar as possible, while halls should be as diverse as possible.

“We had a match that seemed perfect, until we discovered that one was a cattle rancher’s son and the other was a vegan (绝对素食者),” said Ms. Kromm. “They should definitely meet, on the same hall. But we didn’t want to put them in the same room.” Occasionally, an incoming student asks to be paired with an Asian, or says she might not be able to get along with a Republican. In such cases, Ms. Kromm will remind them that Davidson does not accept roommate preferences based on race, ethnicity, and religion.

Davidson’s care in matching pays off. By Christmas last year, only four requested roommate changes out of 480 students. No one knows whether computer-matching works as well. But at Emory, so far, student reaction seems to be overwhelmingly positive.

Around the world more and more people are taking part in dangerous sports and activities. Of course, there have always been people who have looked for adventure – those who have climbed the highest mountains, explored unknown parts of the world or sailed in small boats across the greatest oceans. Now, however, there are people who seek an immediate excitement from a risky activity which may only last a few minutes or even seconds.

I would consider bungee jumping to be a good example of such an activity. You jump from a high place (perhaps a bridge or a hot-air balloon) 200 meters above the ground with an elastic rope tied to your ankles. You fall at up to 150 kilometers an hour until the rope stops you from hitting the ground. It is estimated that two million people around the world have now tried bungee jumping. Other activities which most people would say are as risky as bungee jumping involve jumping from tall buildings and diving into the sea from the top of high cliffs.

Why do people take part in such activities as these? Some psychologists suggest that it is because life in modern societies has become safe and boring. Not very long ago, people's lives were constantly under threat. They had to go out and hunt for food, diseases could not easily be cured, and life was a continuous battle for survival.

Nowadays, according to many people, life offers little excitement. They live and work in comparatively safe environment; they buy food in shops; and there are doctors and hospitals to look after them if they become ill. The answer for some of these people is to seek danger in activities such as bungee jumping.

Mother Teresa was born in Yugoslavia, on August 27, 1910. She attended the government school near her home until she was eighteen. At that time, some doctors and nurses from Yugoslavia were working in India, and they often wrote to the school about their work. She decided to join them one day.

When she left school, she went first to Britain. Then a year later she went to India, where she began to train to be a teacher. After training, she was sent to Calcutta, where she taught geography at a school and soon after became headmistress.

However, although she loved teaching, in 1946 Mother Teresa left the school and went to work in the poor parts of Calcutta. Later she trained to become a nurse in Patna, and then began her work helping the poor and comforting the dying in the streets of the city. Slowly, others came to help her, and her work spread to other parts of India. Mother Teresa is now a well-known person. Many photos have been taken of her, as she travels the world to open new schools and hospitals in poor countries. In 1979, she was given the Nobel Peace Prize for the lifetime of love and service she has given to the poor.