Many kids don't drink enough water daily, according to a new study. The study's lead author, Erica Kenney, at first planned to look into the amount of sugary drinks kids were drinking in schools. However, during her research she found that many kids were simply not drinking enough water.

    Kenney and her team examined data from a group of 4,000 children, aged 6 to19. The data was taken from the National Health and Nutrition Survey, a study on the health of children in the United States done each year by the Center for Disease Control and Prevention.

    While looking through the survey results, she noticed that more than half of the kids who took part in the study were dehydrated (脱水的). Of that group, boys were 76% more likely than girls not to have enough water in their system. Nearly one quarter of the kids in the survey reported drinking no plain water at all.

    “These findings highlight (突出) a possible health issue that wasn't given a lot of attention in the past,” Kenney said in a statement. “Even though for most of these kids this is not an immediate and great health risk, this is an issue that could really be reducing quality of life and well-being for many children and youth.”

    The United States-National Agriculture Library says average kids need between 10 to 14 cups of water every day. This water can come from a mix of drinks and foods that contain high amounts of water, such as celery, melons or tomatoes. It is also suggested that fluids (液体) come from water instead of sugary drinks that are high in calories and can lead to weight problems.

    Contrary to popular belief, people who sleep six to seven hours a night live longer, and those who sleep eight hours or more die younger, according to the latest study ever conducted on the subject. The study, which has tracked the sleeping habits of 1.1 million Americans for six years, weakens the advice of many sleep doctors who have long recommended that people get eight or nine hours of sleep every night.

    “There's an old idea that people should sleep eight hours a night, which has no more scientific basis than the gold at the end of the rainbow,” said Daniel Kripke, professor of psychiatry（精神病学）at the University of California at San Diego who led the study published in a recent copy of JAMA Psychiatry.

    The study was not designed to answer why sleeping longer may be harmful or whether people could extend their lifespan by sleeping less.

    But Kripke said it was possible that people who slept longer tended to suffer from short-term absence of sleeping, a condition where weak breathing puts stress on the heart and brain. He also stressed that the need for sleep was similar to that for food, where getting less than people want may be better for them.

    The study quickly caused warnings and criticism（批评）, with some sleep experts saying that the main problem of America's sleep habits was deprivation（剥夺）, not sleeping too much.

    “None of this says sleep kills people,” said Daniel Buysse, a psychiatrist at the university of Pittsburgh Medical Center.

    “You should sleep as much as you need to feel awake, alert and attentive the next day,” Buysse added. “I'm much more concerned about people short-changing themselves on sleep than people sleeping too long.”

    “Sleeplessness produces a variety of health consequences that were not measured in the study,” critics said.

    See our editors' top 5 picks in print books and Kindle books, and discover our editors' picks for the best books of the year.

    # 1 Killers of the Flower Moon: The Osage Murders and the Birth of the FBI by David Grann

    In Killers of the Flower Moon, David Grami revisits a shocking series of crimes in which dozens of people were murdered in cold blood. Based on years of research and new evidence, the book is a masterpiece of narrative nonfiction.

    Kindle: $14.99 Hardcover: $ 17.37 Paperback: $15.36

    # 2 Little Fires Everywhere by Celeste Ng

    Little Fires Everywhere explores the weight of secrets, the nature of art and identity, and the fierce pull of motherhood and the danger of believing that following the rules can avoid disaster,

    Little Fires Everywhere is the perfect gift for the holidays!

    Kindle: $13.99 Hardcover: $ 20.96 Paperback: $ 12.95

    # 3 Bear Town by Fredrik Backman

    It is a novel about a forgotten town bothered by scandal and the amateur hockey team that might just change everything into a better place. Winning a junior ice hockey championship might mean everything to the residents of Beartown.

Kindle: $10.99 Hardcover: $ 12.95

    # 4 Exit West by Mohsin Hamid

    Profoundly intimate and powerfully inventive, Exit West tells an unforgettable story of love, loyalty, and courage that is both completely of our time and for all time.

Kindle: $12.99 Hardcover: $ 15.73 Paperback: $11

    # 5 Homo Deus: A Brief History of Tomorrow by Yuval Harari

    Yuval Noah Harari, author of the international phenomenon Sapiens, returns with an equally original and attractive book, turning his focus toward humanity's future, and our quest to upgrade humans into gods.

    Kindle: $17.99 Hardcover: $ 28.95 Paperback: $22.99

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    Garden of the Drunken Bai Pond

    With a history of more than 300 years, the Pond of the Drunken Bai, a classical garden in the style of Ming Dynasty, is among the Five Classical Gardens in Shanghai. "Bai" is said to be Li Bai, a famous poet in the Tang Dynasty. However, some believe that "Bai" indicates Bai Juyi, another well-known poet in the Tang Dynasty.

    Zhujiajiao Ancient Town

    Located at the bank of the Dianshan Lake in Qingpu District, Zhujiajiao Ancient Town, with a history of over 1,000 years, has been known as "Venice of Shanghai" for its simple but attractive appearance. Inside the own are rivers and bridges, giving tourists a sense of the ancient time.

    Upside-down House

    In China, the upside-down house is a new thing, but in foreign countries, it is getting more and more popular in recent years, especially in Poland. As is name suggests, the house is built inverted（倒置的）. Inside it, all the furniture and household items are placed upside down. People will feel the magic of a disorder space when walking in the house.

    Chenshan Botanical Garden

    The garden covers a total area of about 206 hectares（公顷）. Its theme is "plant and Health", combining research, education and landscape appreciation. It opened to the public in April, 2010, and is expected to be the largest one in Shanghai.

Tickets: 40 yuan per person; children under l.2m: free of charge if accompanied by an adult.

    Hotshot jet pilots are no match for cliff swallows. The birds rocket over bridges and skim over lakes, rushing forward at accelerations that would knock an Air Force. By tracking these contests with high-speed cameras, a new study gives the first, in-depth peek into avian aerodynamics (鸟类空气力学) in the wild. "The findings may even provide insight into how to design better micro air vehicles-tiny drones. This technology will be brilliantly useful," says biomechanics expert Jim Usherwood of the United Kingdom's Royal Veterinary College in Hatfield. "High-resolution field studies like this have never been done before for birds."

    For cliff swallows, the trouble starts when they return from wintering in South America to their summer homes in North America. After arrival, they seek out their old mud nests—usually located under concrete bridges and freeways-and start rebuilding their homes. But rather than hunt down a fresh supply of mud, some swallows prefer stealing supplies from their more hardworking neighbors. Others take things further and will even lay an egg or two in their neighbor's nest before taking off.

    Battles in the air follow if the invaders are caught in the act, and a new study takes advantage of these fights to learn how birds perform high-speed maneuvers (演习). The team placed three cameras along a North Carolina lake crossed by a highway bridge that houses several cliff swallow nests and waited for the battles to commence.

The team was surprised to learn that most of the time, chasers copied the move of fleeing invaders. Swallows also pull very hard turns to escape an enemy, with one extreme case reaching 7.8 gravity. Fighter pilots usually pass out at about 5 or 6 gravity, which is why these experiments have earned interest, and partial funding, from the Office of Naval Research. The Navy may use the findings to build better guidance systems for micro air vehicles. However, the swallows' biomechanics are complex, and now the team is simply trying to collect a few tricks.

    All of us know that smoking does harm to our health. But do you think everything will be OK as long as you quit smoking?

    Unfortunately, the answer is NO.

    New research has found that even if you give up smoking, the damage it has done to your genes (基因) will stay there for a much longer time. In the research, a team of US scientists studied the blood of 16,000 people. Among them, some were smokers, some used to smoke, and the rest were non-smokers. Scientists compared their genes and found that more than 7, 000 genes of smokers had changed—a number that is one-third of known human genes. According to NBC News, both heart disease and cancer are caused by genetic changes. Some people may have had the changes when they were born, but most people get them in their daily lives while doing things like smoking. When you stop smoking, a lot of these genes will return to normal within five years. This means your body is trying to heal (治愈) itself of the harmful effects of smoking. But the changes in some of the genes stay for longer. They can stay for as long as 30 years, It's almost like leaving a footprint on wet cement (水泥)—it will always be there, even when you've walked away and when the cement becomes dry. Although the study results may make people unhappy, there is a bright side: the findings could help scientists invent medicine to treat genetic damage caused by smoking or find ways to tell which people have heart disease or cancer risks.