Exercise may help to safeguard the mind against depression(沮丧) through previously unknown effects on working muscles, according to a new study involving mice.

    Mental health experts have long been aware that even mild, repeated stress can contribute to the development of depression and other mood disorders in animals and people. Scientists have also known that exercise seems to cushion against depression. But precisely how exercise, a physical activity can reduce someone's risk for depression, a mood state, has been mysterious. So for the new study, researchers at the Karolinska Institute in Stockholm studied the brains and behavior of mice in a complicated and novel fashion.

    We can't ask mice if they are feeling cheerful or in low spirits. Instead, researchers have pictured certain behaviors that indicate depression in mice. If animals lose weight, stop seeking out a sugar solution when it's available — because, probably, they no longer experience normal pleasures — or give up trying to escape from the cold-water zone just freeze in place, they are categorized as depressed. And in the new experiment, after five weeks of frequent but low-level stress, such as being lightly shocked, mice displayed exactly those behaviors. They became depressed.

    The scientists could then have tested whether exercise blunts (延缓) the risk of developing depression after stress by having mice run first. But, frankly, from earlier research, they wanted to know how, so they bred pre-exercised mice. A wealth of earlier research by these scientists and others had shown that aerobic exercise, in both mice and people, increases the production within muscles of an enzyme (酶) called PGC-1alpha. The Karolinska scientists suspected（怀疑） that this enzyme somehow creates conditions within the body that protect the brain against depression. Then, the scientists exposed the animals, which without exercising, were in high levels of PGC-1alpha to five weeks of mild stress. The mice responded with slight symptoms of worry. But they did not develop depression. They continued to seek out sugar and fought to get out of the cold-water zone. Their high levels of PGC-1alpha appeared to make them depression-resistant（抵抗的）. Finally, to ensure that these findings are relevant to people, the researchers had a group of adult volunteers complete three weeks of frequent endurance training, consisting of 40 to 50 minutes of moderate cycling or jogging. The scientists conducted muscle biopsies (活体检查) before and after the program and found that by the end of the three weeks, the volunteers' muscle cells contained substantially more PGC-1alpha than at the study's start.

    The finding of these results, in the simplest terms, is that “you reduce the risk of getting depression when you exercise,” said Maria Lindskog, a researcher at the Karolinska Institute.

    Some materials are obtained from natural resources that are changed by chemical processes in a laboratory. The resulting artificial materials are synthetic, or human-made.

    Plastic is a synthetic substance, obtained from petroleum, a fossil fuel. The molecules（分子）in petroleum are split and then linked into chains. Plastic is an example of a polymer, a material made of repeating patterns of atoms linked together. Most polymers are synthetic. They are made by polymerization, the process of chemically linking many smaller molecules to form a larger molecule that has different physical features. Some polymers, such as proteins, occur naturally.

    Plastic is a key component of many products. When heated into an almost-liquid form, plastic can be made into fibers, sheets, or molds（模具）. It can be mixed with other elements to remain flexible, or it can harden into a solid. Plastic fibers can be made into clothing or carpeting. Sheets of plastic can be made into plates. Molded plastic can be sued for protective helmets or car bumpers.

    Most plastics can be reheated and remolded repeatedly. This feature makes plastic very easy to use. Polymers can be pulled into fine strings or molded into almost any kind of shape. For example, tubes of plastic can be shaped into bottles by different processes. One such process is extrusion blow-molding. Most plastics are also resistant to many chemicals that might harm other materials. This quality is the reason that so many cleaning liquids are packaged in plastic bottles.

    Plastics are good insulators that can stop electricity or heat to pass through. Look around your kitchen, and observe where plastics are used. Pot handles are sometimes made of plastic, as are cooking tools, toaster controls, and microwave cookware. Food-storage wraps and containers may be made of plastic. Take a walk outdoors, and note all the plastic items you see. Gardening tools, such as watering cans and sprayers, are often made of plastic. Swings and slides made of plastic do not become as hot as metal, so they are safer for play. Because plastics can be heated, remolded, and made into something else, they can be recycled and reused.

    A rabbit and two ducks were good friends. They used to meet on the bank of a river and play together. One day the ducks told the rabbit that they had found a carrot farm on the other bank of the river. The rabbit was excited and quickly asked for the help of his friends to cross the river, reach the farm and enjoy the carrots. The ducks agreed to carry him across the river.

    They made a wonderful plan to cross the river. The two ducks entered the river and stayed close to each other. The rabbit carefully got on their backs and stayed still. Then the ducks slowly swam across the river, staying close to each other. The rabbit cautiously stayed on top of the moving birds.

    Right before they reached the center of the river, the ducks suddenly saw a large number of fishes swimming together. In the excitement of finding a delicious meal in the water, the ducks quickly swam to either side to catch the fishes. They forgot about the poor rabbit on their backs, who fell down into the deep river as the ducks moved away. The ducks remembered their job only after they finished their meal. However, by that time the poor rabbit had already drowned (淹死). The foolish ducks were sorry to miss their good friend.

    From this short story, we know love should not be just words and talk; it must be true love, which is shown it in action.

    In the nineteenth century, one of America's greatest writers, Walt Whitman, helped people learn to value poetry. Whitman created a new kind of poetry.

    Walt Whitman was born in eighteen nineteen in New York City. During his long life, he watched America grow from a young nation to the strongest industrial power in the world. As a young man, Whitman worked as a school teacher, a printer and a newspaper reporter. He was thirty-six years old when he published his first book of poetry in eighteen fifty-five. He called it Leaves of Grass. It had only twelve poems. The poems are written in free verse. The lines do not follow any set form. Some lines are short. Some are long. The words at the end of each line do not have a similar sound. They do not rhyme.

    One of America's greatest thinkers and writers immediately recognized the importance of Leaves of Grass. Ralph Waldo Emerson praised Whitman's work. But most other poets and writers said nothing and even denounced it. Most readers also rejected Whitman's poems. The new form of his poetry surprised many people. Even his own brother told Whitman that he should stop writing poetry. But Whitman had many things to say. And he continued to say them. Readers began to understand that America had a great new poetic voice.

    Walt Whitman's poems praise the United States and its democracy. The poet expressed his love for America and its people in many ways. Experts today praise Leaves of Grass as a major literary work. In eighteen seventy-three, Walt Whitman suffered a stroke. He spent the last years of his life in Camden, New Jersey. Whitman was poor and weak during the last years of his life. He died in eighteen ninety-two. Some critics say Walt Whitman was a spokesman for democracy. Others say he was not a spokesman for anything. Instead, they simply call him a great poet.

    For many creatures, the ocean is a terrifying place. Several marine animals have declined as a result of overfishing and pollution. But cephalopods(头足动物) — a type of invertebrate(无脊椎动物) that includes octopuses, cuttlefish, and squid, have seen a dramatic increase in their numbers over the past 60 years.

    Zoe Doubleday, a scientist at the University of Adelaide, in Australia, conducted a study of cephalopods recently. She points out that their population rise is due to the animals' unique traits.

    The creatures can change their color and body shape. They are fast-growing and live for only one or two years. "This allows them to adapt to changing environmental conditions more quickly than other marine species," Doubleday says.

    "Rising sea temperatures may be speeding up the animals' life cycle. They may be growing faster and producing more young."

    Cephalopods live in all of the world's oceans. They can be found in waters from the freezing polar regions to the warm tropic regions. Because they adapt so easily to their environment, the animals are called "the weed of the sea".

    Will octopuses, cuttlefish, and squid take over the world one day? Some people may wonder. According to Doubleday, that is unlikely. The rise in cephalopod populations could slow down if the animals run out of prey(被捕食的动物) and start feeding on one another. Overfishing could also have an impact on their numbers.

    For now, the cephalopod population boom is good news for them and some other sea creatures. "Increases in cephalopod populations could benefit predators(捕食性动物) such as marine mammals and seabirds, which rely on cephalopods for food," Doubleday says.

    Nottingham Goose (鹅) Fair started on the first Thursday in October and lasted 3 days. However, nowadays you won't find any geese there.

    The fair opened at 12: 00 on the Thursday by the Lord Mayor of Nottingham, but it has an interesting and shocking history.

    For starters, it wasn't always the largest fair in the area. And the main fair for the people of Nottingham in terms of trade and economy was the Lenton Fair held at Lenton Priory.

    In the Middle Ages the Lenton Fair overshadowed (使显得逊色) the Goose Fair in size and importance. Harrisons Calendar of Fairs for 1587 mentions the Lenton Fair but not the Goose Fair. However the Goose Fair competed with its local competitors and every year over 20, 000 geese from the Fens in Lincolnshire arrived to be sold to provide the traditional Michaelmas dish.

    It wasn't just for geese either. All kinds of things were sold at the Goose Fair: sheep, horses and cattle were also sold.

    The fair has been under threat of closure many times over the years. In 1764, they actually had cheese riots (暴乱) due to an increase of a third on the price of cheese compared with the previous year, which resulted in an attack on the stallholders (摊主) at the fair.

    By 1880 the fair was reduced to a three-day event, which started on the first Thursday of October. In 1928, the fair was moved from the market square to its present site in the forest which is far away from the city centre. Despite attempts throughout its history to prevent the fair, the income from rents paid by the stallholders is financially beneficial to the local government. So regardless of the cheese riots and the various attempts to prohibit it, Nottingham Goose Fair has survived to celebrate over eight centuries of fun.