If a diver surfaces too quickly, he may suffer the bends. Nitrogen (氮) dissolved (溶解) in his blood is suddenly liberated by the reduction of pressure. The consequence, if the bubbles (气泡) accumulate in a joint, is sharp pain and a bent body—thus the name. If the bubbles form in his lungs or his brain, the consequence can be death.

    Other air-breathing animals also suffer this decompression (减压) sickness if they surface too fast: whales, for example. And so, long ago, did ichthyosaurs. That these ancient sea animals got the bends can be seen from their bones. If bubbles of nitrogen form inside the bone they can cut off its blood supply. This kills the cells in the bone, and consequently weakens it, sometimes to the point of collapse. Fossil (化石) bones that have caved in on themselves are thus a sign that the animal once had the bends.

    Bruce Rothschild of the University of Kansas knew all this when he began a study of ichthyosaur bones to find out how widespread the problem was in the past. What he particularly wanted to investigate was how ichthyosaurs adapted to the problem of decompression over the 150 million years. To this end, he and his colleagues traveled the world's natural-history museums, looking at hundreds of ichthyosaurs from the Triassic period and from the later Jurassic and Cretaceous periods.

    When he started, he assumed that signs of the bends would be rarer in younger fossils, reflecting their gradual evolution of measures to deal with decompression. Instead, he was astonished to discover the opposite. More than 15% of Jurassic and Cretaceous ichthyosaurs had suffered the bends before they died, but not a single Triassic specimen (标本) showed evidence of that sort of injury.

    If ichthyosaurs did evolve an anti-decompression means, they clearly did so quickly—and, most strangely, they lost it afterwards. But that is not what Dr Rothschild thinks happened. He suspects it was evolution in other animals that caused the change.

    Whales that suffer the bends often do so because they have surfaced to escape a predator (捕食动物) such as a large shark. One of the features of Jurassic oceans was an abundance of large sharks and crocodiles, both of which were fond of ichthyosaur lunches. Triassic oceans, by contrast, were mercifully shark- and crocodile-free. In the Triassic, then, ichthyosaurs were top of the food chain. In the Jurassic and Cretaceous, they were prey (猎物) as well as predator—and often had to make a speedy exit as a result.

    In the U.S., speaking more than one language fluently is not very common — except in Los Angeles, California. The city has one of the largest populations in the U.S. of young people between the ages of 18 and 34. More than half of them in Los Angeles are bilingual (会说两种语言的).

    Maria Elena Burgos, a mother of two American-born daughters, is cooking a Mexican breakfast. She says making Mexican food is just one of the many traditions in her home. Another is speaking Spanish to her children. “We want to keep Spanish somewhere in their learning too, not only at home.” Ms. Burgos thinks being bilingual will give them more opportunities in the competitive world. Knowing Spanish also means the children can talk with their relatives in Mexico.

     Ms. Burgos' daughters both want to know their family's culture. “We are doing this in order to go back to our roots because that's part of who we are,” they say.

    The U.S. Census Bureau (人口普查局) says more than half the adults in the Los Angeles area between 18 and 34 years old speak a language other than English at home. For the whole country, the number of bilingual adults is only 25 percent. The number of bilingual speakers has gone up since the 1990s.

    University of California Los Angeles professor Raul Hinojosa says that in the past, the children and grandchildren of immigrants (移民) did not continue to speak the parents' native language. But now the opposite is true.

    In the last ten years, more immigrant parents say they want their children to keep speaking their native language. Mr. Hinojosa calls their choice the “path of pride”. The decision to keep a native language is clear in Los Angeles now. And, as the number of minorities in the U.S. continues to grow, he thinks bilingualism will spread to the rest of the country.

    It's school time again! You're probably feeling excited and maybe a little sad that summer is over. Some kids feel nervous or a little scared (害怕的) on the first day of school because of all the new things: new teachers, new friends, and even a new school. Luckily, these "new" worries only stick around for a little while. Let's find out more about going to a new school.

    Most teachers kick off the new school year by introducing themselves and talking about all the stuff you'll be doing that year. Some teachers give students a chance to tell something about themselves to the rest of the class, too. When teachers do the talking on the first day, they often go over classroom rules and school rules so you'll know what's allowed and what's not. Please pay close attention.

    You might already know a lot of people in your classes on the first day, but it's a great day to make new friends, so try to say hello to kids you know and new ones that you don't. Make the first move and you'll be glad, and so will your new friends!

    Seeing friends you haven't seen in a while can make the first day a good one. You can make the day feel special by wearing clothes that you really like. Maybe you got a great T-shirt on one of your vacations, or a pair of sneakers (运动鞋). It also can make you feel good to be prepared and have all the things you need, such as pencils, folders, and whatever else you'll be needing. But make sure that you pack them the night before in case you don't have time in the morning.

    A new "paparazzi-proof" scarf has got heatedly welcomed since launched. A new "paparazzi-proof" scarf could be a game-changer for celebrities who prefer to shy away from the stage light. The ISHU scarf is the creation of Dutch-born fashion entrepreneur Saif Siddiqui and is designed to "give people their right to privacy back". A host of celebrities including Cameron Diaz, singer Joe Jonas, Bayern Munich footballer Jerome Boateng and music producer Major Lazer have worn the ISHU after it was spotted at London Fashion Week last year.

    It works by reflecting the light back into a camera, effectively becoming "invisibility clothes" for celebrities who don't want their photos taken. Anyone wearing the scarf is protected from mobile flash photograph, with the fashion accessory's fabric (附件结构) effectively blocking out any unwanted pictures, although it doesn't stop no-flash photographs from being taken.

    The 28-year-old Siddiqui was inspired while visiting family in Amsterdam in 2009 when his friends attempted to take a photo of him using an iPhone in front of some bikes. "He noticed that the bike's reflector carried the flash of his mobile camera in a way that confused the faces of his friends in the picture." the ISHU website explains. "He immediately realized that if developed into the right product, this feature would be an ideal solution for his friends and is now available to the public who want to keep their private moments in public private. "Saif put together a team of experts who dug into the science of light and reflection, and how to blend technology with fashion."

    He told Decoded Magazine: "The ISHU scarf effectively allows an individual to control what pictures and videos are taken of him. "There are no more unwanted pictures and videos on Snapchat, Instagram, or Facebook! Everyone carries a phone with them nowadays that has an amazing camera. So, it all made sense to me." More ISHU products are set to launch in August, with mobile phone cases set to launch in the next few weeks. The ISHU is currently sold out but you can pre-order it online for ￡289.

As the experts say,swimming is an excellent way to work your entire body.An hour of swimming{#blank#}1{#/blank#} (burn) almost as many calories as running.There are a host of benefits you may gain from swimming{#blank#}2{#/blank#} (regular).

One of{#blank#}3{#/blank#} biggest benefits of swimming is that it truly works well from head to toe.It can not only increase your heart rate without{#blank#}4{#/blank#} (stress) your body,but also build up your muscles and strength.Besides,swimming makes your heart and lung strong.{#blank#}5{#/blank#} (research) say that it may even reduce your risk of death.{#blank#}6{#/blank#} (compare) with inactive people,swimmers have about half the risk of death.Some other studies have shown that swimming may help lower blood pressure and control blood sugar.

The number of persons{#blank#}7{#/blank#} experience some level of insomnia (失眠症) is increasing,so this is excellent news—the researchers conclude that swimming is a potentially powerful way{#blank#}8{#/blank#} (relieve) stress quickly and promote deeper sleep.

As with any workout,there are certain risks associated with swimming.If you{#blank#}9{#/blank#} (injure) or have certain medical conditions,be sure to check with your doctor before swimming.{#blank#}10{#/blank#} general,it's a good idea to check with your doctor whenever you start a new exercise program.

Living a healthy lifestyle is all about choosing to make healthy choices each day. Here are some tips on how to improve your physical, mental, and emotional health.

Set specific and actionable goals to improve your health. When you have specific goals you want to achieve, you'll be more motivated to implement（实施） healthy changes in your life. {#blank#}1{#/blank#} And then set goals that are specific, measurable, attainable, relevant, and time-bound to better guarantee your success.

{#blank#}2{#/blank#}. It's no secret that healthy eating is one of the keys to achieving a healthy lifestyle. When you follow a healthy diet, you reduce your risk for obesity, heart disease, type 2 diabetes, high blood pressure, and certain types of cancers. Healthy eating can also improve your mood and make you happier.

Make a conscious effort to drink enough water throughout the day. Just like nutritious foods, water is essential to keeping your body healthy.{#blank#}3{#/blank#} For adults, drinking around 13 cups of water a day is enough, but this amount can vary depending on your age, weight, environment, and physical activity level.

Aim for at least 7 hours of quality sleep each night.{#blank#}4{#/blank#} It helps you maintain a healthy weight, and improve your overall mood. Most adults need at least 7 hours of quality sleep each night, and children need 8 to 13 hours depending on how old they are.

Find a type of physical activity that's enjoyable for you. The benefits of physical activities are endless. Doing physical activities lowers your risk of things like stroke and high blood pressure, helps you lose weight, and improves your cognitive（认知的） function.{#blank#}5{#/blank#}.

A. Consult the doctor about your physical condition.

B. Choose nutritious foods and create a well-balanced diet.

C. Identify what parts of your lifestyle you want to improve.

D. Choose activities that make you feel happy and confident.

E. Water benefits your digestion and keeps you from getting thirsty.

F. What's more, being active can improve your overall mental health.

G. A good night's sleep is good for your health and attention during the day.