Man has been to the moon. It has been the first step towards future exploration in space. When compared with the distances between Earth and the other planets, the distance between the Moon and Earth is very short indeed. Mars, the nearest planet to Earth is millions of miles away! Traveling to the planets will be man's next step. Such travels will be more challenging than the trip to the moon and certainly more exciting and dangerous. Recently, two American spaceships, Viking 1 and 2, landed on Mars trying to discover whether that planet has any life on it. So far the signs of life on Mars has neither been confirmed nor ruled out (排除). Russians have discovered that the surface of Venus is so hot that it is almost certain that there is no life there. Also the atmosphere of Venus is extremely dense and the pressure is nearly a hundred times greater than that of the Earth's atmosphere. Scientists believe man may find planets which have the same conditions as those we have on Earth, but man should realize Earth will be his only home for a long time and begin to love and care for it.

    Popular music in America is what every student likes. Students carry small radios with earphones and listen to music before class, after class, and at lunch. Students with cars buy large speakers and play the music loudly as they drive on the street.

    Adult(成年人) drivers listen to music on the car radio as they drive to work. They also listen to the news about sports, the weather, and the life of American people. Most of the radio programmers（节目）are music.

    Pop or popular music singers make much money. They make a CD or tape which radio stations use in many places. Once the popular singer is heard all over the country, young people buy his or her tapes. Some of the money from these tapes goes to the singer. Wherever the singer goes, all the young people want to meet him or her. Now the singer has become a national star.

    There are other kinds of music that are important to Americans. One is called folk music. It tells stories about the common life of Americans. Another is called western or country music. This is started by cowboys（牛仔）who would sing at night to the cows they were watching. Today, any music about country life and the love between a country boy and his girl is called western or country music.

    Along the river banks of the Amazon and the Orinoco there lives a bird that swims before it can fly, flies like a fat chicken, eats green leaves, has the stomach of a cow and has claws(爪) on its wings when young. They build their homes about 4.6m above the river, an important feature(特征) for the safety of the young. It is called the hoatzin(麝雉).

    In appearance, the birds of both sexes look very much alike with brown on the back and cream and red on the underside. The head is small, with a large set of feathers on the top, bright red eyes, and blue skin. Its nearest relatives are the common birds, cuckoos. Its most striking feature, though, is only found in the young.

    Baby hoatzins have a claw on the leading edge of each wing and another at the end of each wing tip. Using these four claws, together with the beak(喙), they can climb about in the bushes, looking very much like primitive birds. When the young hoatzins have learned to fly, they lose their claws.

    During the drier months between December and March hoatzins fly about the forest in groups of 20 to 30 birds, but in April, when the rainy season begins, they collect together in smaller living units of two to seven birds for producing purposes.

    When Kevin Durant gave his tearful MVP speech in 2014, the NBA star made sure to thank one person who had been there with him from the very beginning: his mother. His heartfelt words about the sacrifices she made for Durant and his brother led to a lifetime movie about her journey as a single parent, The Real MVP: The Wanda Durant Story.

    Today, the NBA superstar's mom travels the country as a motivational speaker and philanthropist (慈善家). On Monday, she spoke at Thomson Reuters' in New York about her personal struggles to achieve financial stability and shared the financial advice she gave her son when he entered the league with CNBC.

    “I wanted him to realize he has worked hard," she says, "And it is OK for him to enjoy himself because of his hard work. But it is also imperative that he prepares for his future.” While she advised him to enjoy the rewards of his labor, she also wanted to make sure that her son knew the importance of financial planning.

    She told the audience that when she found herself a single parent to two children at 21, she couldn't follow the financial principles. Rather than planning for the future, she focused only on how her money could make ends meet for that moment.

Recently, Durant has teamed up with Laurene Powell Jobs for a new philanthropic program called College Track which is aimed at helping disadvantaged kids attend college. As part of the program, Durant has committed to donating $10 million to his hometown's public school system.

    Durant's mom says that in addition to his financial decisions, she is proud of his philanthropic work and his desire to help the community. “I thought giving back was always very important, and so we talked about that and he had seen that from us as a family and it's one of the things that I taught him," she says.

    For thousands of years, people have known that the best way to understand a concept is to explain it to someone else. "While we teach, we learn," said Roman philosopher Seneca. Now scientists are bringing this ancient wisdom up to date. They're documenting why teaching is such a fruitful w ay to learn, and designing creative ways for young people to take part in instruction.

    Researchers have found that students who sign up to tutor others work harder to understand the material, recall it more accurately and apply it more effectively. Student teachers score higher on tests than pupils who're learning only for their own sake. But how can children, still learning themselves, teach others? One answer: They can tutor younger kids. Some studies have found that first-born children are more intelligent than their later-born siblings(兄弟姐妹). This suggests their higher IQs result from the time they spend teaching their siblings. Now educators are experimenting with ways to apply this model to academic subjects. They arrange college undergraduates to teach computer science to high school students, who in turn instruct middle school students on the topic.

    But the most cutting-edge tool under development is the "teachable agent" — a computerized character who learns, tries, makes mistakes and asks questions just like a real-world pupil.

    Computer scientists have created an animated(动画的)figure called Betty's Brain, who has been "taught" about environmental science by hundreds of middle school students. Student teachers are inspired to help Betty master certain materials. While preparing to teach, they organize their know ledge and improve their own understanding. And as they explain the information to it, they identify problems in their own thinking.

    Feedback from the teachable agents further improves the tutors' learning. The agents' questions forces student tutors to think and explain the materials in different ways, and watching the agent solve problems allow s them to see their know ledge put into action.

    Above all, it's the emotions one experiences in teaching that improve learning. Student tutors feel upset when their teachable agents fail, but happy when these virtual pupils succeed as they develop pride and satisfaction from someone else's accomplishment.

    The negative (负面的) health effects of sleep shortages during the week can't be changed by marathon weekend sleep sessions, according to a new study.

    Researchers have long known that routine sleep deprivation (缺乏) can cause weight gain and increase other health risks, including diabetes. But there are still some people who hope that shutting off the alarm on Saturday and Sunday will repay the weekly sleep debt and remove any ill effects.

    The research, published in Current Biology, ruins those hopes. Despite complete freedom to sleep in and nap during a weekend recovery period, participants in a sleep laboratory who were limited to five hours of sleep on weekdays gained nearly three pounds over two weeks and experienced metabolic disruption (代谢紊乱) that would increase their risk for diabetes over the long term. While weekend recovery sleep had some benefits after a single week of inadequate sleep, those gains were wiped out when people returned right to their same sleep schedule the next Monday.

    "If there are benefits of catch-up sleep, they're gone when you go back to your routine. It's very short-lived," said Kenneth Wright, who led the research. "These health effects are long-term. It's kind of like smoking once was — people would smoke and wouldn't see an immediate effect on their health, but people will say now that smoking is not a healthy lifestyle choice. I think sleep is in the early stage of where smoking used to be."

    Wright said that the study suggests people should prioritize sleep — cutting out the optional "sleep stealers" such as watching television shows or spending time on electronic equipment. Even when people don't have a choice about losing sleep due to child-care responsibilities or job schedules, they should think about prioritizing sleep in the same way they would think about a healthy diet or exercise.