Getting less sleep has become a bad habit for most American kids. According to a new survey(调查) by the National Sleep Foundation, 51% of kids aged 10 to 18 go to bed at 10 pm or later on school nights, even though they have to get up early. Last year the Foundation reported that nearly 60% of 7- to 12-year-olds said they felt tired during the day, and 15% said they had fallen asleep at school.

    How much sleep you need depends a lot on your age. Babies need a lot of rest: most of them sleep about 18 hours a day! Adults need about eight hours. For most school-age children, ten hours is ideal(理想的). But the new National Sleep Foundation survey found that 35% of 10- to 12-year-olds get only seven or eight hours. And guess what almost half of the surveyed kids said they do before bedtime? Watch TV.

“More children are going to bed with TVs on, and there are more opportunities(机会) to stay awake, with more homework, the Internet and the phone,” says Dr. Mary Carskadon, a sleep researcher at Brown University Medical School. She says these activities at bedtime can get kids all excited and make it hard for them to calm down and sleep. Other experts say part of the problem is chemical. Changing levels of body chemicals called hormones not only make teenagers' bodies develop adult characteristics, but also make it hard for teenagers to fall asleep before 11 pm.

Because sleepiness is such a problem for teenagers, some school districts have decided to start high school classes later than they used to. Three years ago, schools in Edina, Minnesota, changed the start time from 7:25 am to 8:30 am. Students, parents and teachers are pleased with the results.

    One day a few years ago, a very funny thing happened to a neighbour of mine. He is a teacher at one of London's big medical schools. He had finished his teaching for the summer term and was at the airport on his way to Russia to give a lecture.

    He had put a few clothes and his lecture notes in his shoulder bag , and he had put Rupert , the skeleton (人体骨架）to be used in his lecture , in a large brown suitcase. At the airport desk, he suddenly thought that he had forgotten to buy a newspaper. He left his suitcase near the desk and went over to the shop.

    When he got back he discovered that someone had taken his suitcase by mistake. He often wonders what they said when they got home and found Rupert.

    Here are some schools in Southeast England. Find out if you are interested in any of them.

    PTSD(战后创伤) is sadly a common affliction(折磨) for many soldiers who have witnessed conflict, an invisible wound that continues to cause incredible suffering long after the guns have fallen silent.

    "A lot of us come home without realizing we are bringing the war home with us," said Josh Marino, a veteran (退伍兵)of the Iraq war who suffered the effects of PTSD of suicide .

    "I didn't want to deal with it anymore," Marino said. He wrote a goodbye note, grabbed a knife and went outside for a final cigarette in the rain. But then, from the deepest depth of despair came hope. Meowing out of the bushes next to him came a stray black and white kitten (小猫) which, according to Marino, "just walked up and started rubbing up against my leg and let me pet him. I came to life again and I broke down crying. I burst into tears."

    From this accidental encounter everything changed. Marino found a new purpose in life through the friendly cat, who he named Scout, and who he credits with saving his life. "I stopped thinking about all my problems, and started thinking about all his problems, and what I could do to help him, "Marino said. The bond between them was instant，but that wasn't the end of the story.

    Marino has made a video of his and Scout's remarkable story of healing and heartbreak which you can watch on the Internet. The story is dedicated to showing how animals can help humans through tough times, as well as humans can help them. It is a beautiful story that is sure to tug at your heart strings, showing just how powerful the bond between humans and animals can be. We love it, and we hope you do too!

    A voyaging ship was wrecked during a storm at sea and only two of the men aboard were able to swim to a small, desert-like island. Not knowing what else to do, the two survivors agreed that they had no alternative than to pray to God.

    However, to find out whose prayers were more powerful, they agreed to divide the territory between them and stay on opposite sides of the island.

    The first thing they prayed for was food. The next morning, the first man saw a fruit-bearing tree on his side of the island, and he was able to eat its fruit. But the other man's parcel of land remained barren.

    After a week, the first man became lonely and decided to pray for a wife. The next day, another ship was wrecked and the only survivor was a woman who swam to his side of the island. But on the other side of the island, there was nothing.

    Soon thereafter the first man prayed for a house, clothes and more food. The next day, like magic, all of these things were given to him. However, the second man still had nothing.

    Finally, the first man prayed for a ship so that he and his wife could leave the island, and in the morning he found a ship docked at his side of the island.

    The first man boarded the ship with his wife and decided to leave the second man on the island, considering the other man unworthy to receive God's blessings since none of his prayers had been answered.

    As the ship was about to leave, the first man heard a voice from Heaven booming, "Why are you leaving your companion on the island?"

    "My blessings are mine alone since I was the one who prayed for them," the first man answered. "His prayers were all unanswered and so he doesn't deserve anything."

    "You are mistaken!" the voice rebuked him. "He had only one prayer, which I answered. If not for that, you would not have received any of my blessings."

    "Tell me," the first man asked the voice, "what did he pray for that I should owe him anything?"

    "He prayed that all your prayers would be answered."

    For all we know, our blessings are not the fruits of our prayers alone, but those of another praying for us. So what you do for others is more important than what you do for yourself.

    Throughout much of human history, man has been the measure of many, if not all, things. Lengths were divided up into feet and smaller units from the human hand. Other measures were equally characteristic. Mediterranean traders for centuries used the weight of grains of wheat to define (定义) their units of mass. The Romans used libra, forerunner of the pound, by referring to the weight of a carob (角豆树) seed.

    The sizes of similarly named units could also differ. The king's foot, used in France for nearly

    1,000 years after its introduction by Charlemagne in around 790 AD, was, at 32.5cm,around a centimeter shorter than the Belgic foot, used in England until 1300.Greek,Egyptian and Babylonian versions of water in a fixed container varied from one another by a few kilos, Nor was there agreement on such things within countries. In France, where there was no unified (统一的) measurement system at the national level, the situation was particularly terrible. The lieue (former measure of distance), for example, varied from just over 3 km in the north to nearly 6 km in the south.

    Although John Wilkins, an Englishman, first put forward a decimal system (十进制) of measurement in 1668,it was the French who in 1799 made it law. The Système International d'Unités (SI, or the metric system, as it is better known) developed from it and became the official measurement in all countries except Myanmar, Liberia and the United States. Now the International Bureau of Weights and Measures in Paris is set to give the metric system its biggest shake-up yet.

    At a meeting in Versailles, France, on November 16th,2018,the world's measurement bodies are almost certain to approve a decision that will mean four out of the seven base SI units, including the kilogram, will follow the other three, including the metre, in being redefined in terms of the values of physical constants (物理常数).Each of the chosen constants has been measured incredibly precisely, which would mean that from May 20^th 2019 the constants will themselves be fixed at their current values for ever. Any laboratory in the world will then be able to measure, for example, the mass of an object as precisely as the accuracy of their equipment will allow.