Children in the United States eat too much pizza that some researchers now argue the food should join the ranks of sugary drinks and fast food for the harm they do to health．

    In a new study, the researchers found that pizza is a large source of calories, saturated fat(饱和脂肪)and salt in children's diets．Children should not eat more than two slices of pizza for a meal，and should pair that with salad, rather than with another high-calorie food，the researchers concluded．

    “Parents should aim to control pizza consumption(消费), particularly as a snack where it was shown to have a very adverse impact on children, and they should put their pizza dollars toward healthier brands．”Said Lisa Powel, director of the Illinois Prevention Research Center．

    Pizza has become a matter of focus in recent years for researchers who look at the meals children eat, rather than the nutrients within them．Studies have found pizza is among the greatest sources of calories for children．

    “Since pizza remains a common part of children's diet, we need to make 'healthy' pizza．”Powel said．To make pizza healthier, food producers should reduce its saturated fat and salt, and increase its whole grain content,” she said．

    Whether or not pizza is harmful enough to be picked out as an unhealthy food, the study attracts attention to a larger issue with the modern American lifestyle, said Alexis Tindall, who was not involved in the flow research. “Many foods are eaten too frequently and in large sizes,” said Tindall．To solve the problem, people don't have to give up eating pizza, but instead, they can eat smaller and healthier pizza，”she said．

    “Make it at home, instead of ordering it out where you don't have any control over how it's made.” Tindall said. “When we make it at home, we can choose healthier ingredients，increase the vegetables, reduce fat, and put in less cheese．Pizza doesn't have to be just pepperoni(意大利辣香肠)and cheese．”

    The advice offered from any other 82-year-olds might have made young people yawn and roll their eyes. But when former South African president Nelson Mandela advised two dozen local youth leaders in Los Angeles to take education seriously, his audience was listening.

    The famed old man said to the young people that if they expected to improve the lives of others in the future, they must work at improving their own lives now. "Education is one of the most important weapons you have,” Mandela advised. “It will place you in a far better position to serve yourself and your community.”

“The point is, he was young once and rebellious(叛逆的)once and he kept his dream alive, just as you each have dreams,” explained South Africa's ambassador to the United States, Sheila Sisulu, as she introduced Mandela to the young crowd.

    Asked for specific advice about changing society by 21-year-old Ahmed Younis, Mandela suggested that somehow helping arouse more American interest in foreign affairs might be a start.

There is an impression that Americans, in general, have not followed international developments properly, Mandela said. “I'm not making that statement myself, but there are serious political analysts who say Americans are not well informed as to what has happened in the world.”

22-year-old Omari Trice said Mandela left him full of enthusiasm. “ He's a person who set the tone for an entire nation, said Trice. “You come away feeling you need to be a superman in order to get things done.”

    People born in winter are more likely to suffer mental health disorders, according to a recent study carried out by researchers at Vanderbilt University in Tennessee.

    Researchers raised baby mice from birth to weaning (断奶) in either “summer” light cycles of 16 hours of light and 8 hours of dark or “winter” cycles of 8 hours of light and 16 hours of dark. A third group experienced 12 hours of light and 12 hours of dark a day.

    Then half the winter mice stayed in a winter cycle, while half switched to a summer schedule. The summer mice were similarly split. The mice raised in equal periods of light and dark were split into three groups, one of which stayed on the 12­hour schedule, one of which joined the winter group, and one of which joined the summer group.

    After 28 days, it turns out the summer­born mice behaved the same whether they stayed on the summer cycle or switched to winter. But among the winter­born mice, those that stayed in winter kept their previous schedule, while those that switched to summer stayed active for an extra hour and a half, which indicates that mice born and weaned in a winter light cycle showed dramatic disruptions（破坏） in their biological clocks.

    The finding is the first of its kind in mammals, and it could explain why people born in winter are at higher risk for mental health disorders.

    “We know that the biological clock regulates(管理) mood in humans,” said study researcher McMahon. “If the mechanism (机制) similar to the one that we found in mice operates in humans, then it could not only have an effect on a number of behavioral disorders, but also have a more general effect on personality.”

    The evidence for harmony may not be obvious in some families. But it seems that four out of five young people now get on with their parents, which is the opposite of the popularly held image of unhappy teenagers locked in their room after endless family quarrels.

    An important new study into teenage attitudes surprisingly shows that their family life is more harmonious than it has ever been in the past.” We were surprised by just how positive today's young people seen to be about their families,” said one member of the research team. “They're expected to be rebellious(叛逆的) and selfish but actually they have other things on their minds; they want a car and material goods, and they worry about whether school is serving them well. There's more negotiation and discussion between parents and children, and children expect to take part in the family decision-making process. They don't want to rock the boat.”

    So it seems that this generation of parents is much more likely than parents of 30 years ago to treat their children as friends. “My parents are happy to discuss things with me and willing to listen to me,” says 17-years-old Daniel Lazall. “I always tell them when I'm going out clubbing. As long as they know what I'm doing, they're fine with it.” Susan Crome, who is now 21, agrees.”Looking back on the last 10 years, there was a lot of what you could call negotiation. For example, as long as I'd done all my homework, I could go out on a Saturday night. But I think my grandparents were a lot stricter with my parents than that.”

    Maybe this positive view of family life should not be unexpected. It is possible that the idea of teenagers' rebellion is not rooted in real facts. A researcher comments, “Our surprise that teenagers say they get along well with their parents comes because of a brief period in our social history when teenagers were regarded as different beings. But that idea of rebelling and breaking away from their parents really only happened during that one time in the 1960s when everyone rebelled. The normal situation throughout history has been a smooth change from helping out with the family business to taking it over.”

    Laughter is part of the universal human vocabulary. All members of the human species understand it. Unlike English or French or Swahili, we don't have to learn to speak it. We re born with the capacity to laugh.

    Very little is known about the specific brain mechanisms responsible for laughter. Contrary to folk wisdom, most laughter is not about humor; it is about relationships. To find out when and why people laugh, I went with several assistants to local malls and recorded what happened just before people laughed. Over a 10-year period, we studied over 2, 000 cases of naturally occurring laughter.

    We found that most laughter does not necessarily follow jokes. People may laugh after a variety of statements, such as, "Here comes Mary," "How did you do on the test?" or "Do you have a rubber band?" These certainly aren't jokes.

    We believe laughter evolved from the panting (喘气的) behavior of our ancient ancestors. Today, if we tickle (使发痒) chimps, they don't laugh. But, instead, they produce a panting sound. That's the sound of ape laughter, and it's the root of human laughter.

    Apes laugh in the kinds of situations that lead to human laughter, like games that involve chasing. Other animals produce sounds during play, but they are so different from laughter. Rats, for example, produce high sounds during play and when tickled, but these are very different in sound from human laughter.

    Laughter is often positive, but it can be negative too. There's a difference between "laughing with" and "laughing at". People who laugh at others may be trying to drive them out of the group.

    No one has actually counted how much people of different ages laugh, but young children probably laugh the most. At ages 5 and 6 we probably laugh more than at any other times. Adults laugh less than children, probably because they play less.

    Work now underway will tell us more about the brain mechanisms behind laughter, how it has evolved, and why we're so susceptible to tickling.

    All of us spend a large part of our lives at home — eating, sleeping, relaxing and communicating with our family members. Our home is a shelter for us, away from the noisy, busy, and polluted world outside — a place where we can let down our hair and dress casually. Eco­friendliness (环保) is a hot word today and we all know we should make our environment as eco­friendly as possible. This is not only good for our health, but also good for the outward environment. Here are some easy and helpful tips to make your home eco­friendly.

    Kitchen

    Plan the kitchen to be bright and airy so that you don't have to turn on the lights at daytime. Don't make wasteful use of the gas. Keep all ingredients for cooking ready before lighting the gas. Turn it to low when not required — always using it on "high" burns a lot of gas.

    Indoor plants

    Plants are extremely eco­friendly and can be used to make your home look lively. Apart from adding life to home, they give out O_2, thus making the air inside fresh. You can keep plants in your home, but be sure to show them some sunlight regularly. Also, if they are kept outside, clean their leaves with a wet cloth, as dust may be added to them. A home decorated (装饰) with plants looks attractive. Plants are a natural home decorating gift that shows concern about the environment. A green plant is a wonderful gift which will protect the earth and is sure to be appreciated.

    Saving water

    Most of the time, we take water for granted — we keep water running while brushing our teeth or washing clothes. Needless to say, this is a huge waste of natural resources (资源). Try to recycle water. For example, the water used for washing vegetables can be used for watering plants; the soapy water used for washing clothes can be used to clean the bathroom and kitchen.