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    Sleep, as we know, is important to us because it helps restore tired organs and tissues in our body. But how much sleep do we actually need?

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    For most of us, eight hours seems to be about the right amount. Yet we know that there are a great many people who get along perfectly with less sleep and some who may even need more. A great deal depends on the way we live. But a good general rule to follow is to sleep as long as we have to in order to feel happy and be able to work at our best when we are awake.

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    There are actually different levels of sleep. There is a deep sleep and a shallow sleep. In a shallow sleep our body does not get the same kind of rest as it gets in a deep sleep, so that after eight hours of a shallow sleep we may still feel tired. But a short deep sleep can be very restful.

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    Alexander the Great was able to get a deep sleep whenever he needed it. Once, during the night before an important battle, he remained awake longer than anyone else. Then he wrapped himself in a cloak and lay down on the earth. He slept so deeply that his generals had to wake him three times to give command to attack!

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    Normally when we go to sleep, our “ sleep center” blocks off nerves so that both our brain and our body go to sleep. One prevents us form wanting to do anything and the other makes our internal organs and limbs go to sleep. But someone will fall asleep (brain sleep) and keep on marching, because his body is not asleep!

    My heroes are the Singapore Women's Everest Team．In 2009，they became the first all-women team to climb Mount Everest．The team of six young women trained for seven years before they climbed the mountain．It was difficult for them to train because Singapore doesn't have any snow or any mountains．But they didn't stop，and in the end they made it．They Worked hard every day for their dream so I really admire them．

——Lance Reed, 16, from Britain

    My mum，Mary Evans，is a real hero．I have a very big family, with two brothers and three sisters．My mum works very hard every day to look after us, and she is very busy．She always makes time for everyone and she always listens to me if I have a problem．I really respect my mum because she always looks after my family and makes sure we have everything we need．

——Mark Sterling，l7，from America

    I admire the Salwen family from Atlanta，USA．In 2006, they made a very unusual choice．They decided to sell their house and give half of the money to charity(慈善)．They moved into a smaller house and gave $800,000 to charities in Ghana. I really respect them because they gave their money to people in need．

——William Kloster, 17, from Canada

    I really admire Steve Jobs, the former CEO of Apple．He invented a new kind of technology．Apple technology is very intelligent(智能的)．The products that he made are also really beautiful．Steve Jobs created a successful business in IT．I was very sad when he died in October 2011．I respect him because he changed the way people use technology all over the world．

——Richard Hale, 18，from Australia

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    A team of engineers at Harvard University has been inspired by Nature to create the first robotic fly. The mechanical fly has become a platform for a series of new high-tech integrated systems. Designed to do what a fly does naturally, the tiny machine is the size of a fat housefly. Its mini wings allow it to stay in the air and perform controlled flight tasks.

    “It's extremely important for us to think about this as a whole system and not just the sum of a bunch of individual components (元件),” said Robert Wood, the Harvard engineering professor who has been working on the robotic fly project for over a decade. A few years ago, his team got the go-ahead to start piecing together the components. “The added difficulty with a project like this is that actually none of those components are off the shelf and so we have to develop them all on our own,” he said.

    They engineered a series of systems to start and drive the robotic fly. “The seemingly simple system which just moves the wings has a number of interdependencies on the individual components, each of which individually has to perform well, but then has to be matched well to everything it's connected to,” said Wood. The flight device was built into a set of power, computation, sensing and control systems. Wood says the success of the project proves that the flying robot with these tiny components can be built and manufactured.

    While this first robotic flyer is linked to a small, off-board power source, the goal is eventually to equip it with a built-in power source, so that it might someday perform data-gathering work at rescue sites, in farmers' fields or on the battlefield. “Basically it should be able to take off, land and fly around,” he said.

    Wood says the design offers a new way to study flight mechanics and control at insect-scale. Yet, the power, sensing and computation technologies on board could have much broader applications. “You can start thinking about using them to answer open scientific questions, you know, to study biology in ways that would be difficult with the animals, but using these robots instead,” he said. “So there are a lot of technologies and open interesting scientific questions that are really what drives us on a day to day basis.”

    Does stress cause gray hair? Many people believe that tension and stress can cause your hair to lose its color. In fact, it is an old-wives' tale that being upset all the time can result in premature graying. Here is a closer look at this situation and why some believe that this old wives' tale could be true.

    As one ages, the hairs on the head also age. In fact, just about everything on the human body begins to show signs of wear and tear (磨损) after a while. The joints wear and become stiff and skin wears and becomes wrinkled. Hairs on the head grow and eventually die. They are replaced, but in the process something else happens.

    When new hairs are replacing the old ones, the color or pigment (色素) is also added to them. However, as one ages, this pigment becomes less and less available. At first, hairs will have a limited amount of pigment and they will appear to be grayish in color. In time, they will lose all of their pigment and will be white. Many things are known to cause graying, and genetics is a very powerful factor. If one of your parents turns gray at an early age, there is a good chance that you will too. Some people begin the graying process in high school, while others may be over the age of forty.

    Constant worry and tension can have many harmful effects on the human body. It is a known fact that stressful times can cause one to suffer hair loss. It would make sense that if it can cause these problems, perhaps it also may contribute to graying. However, there is no sound evidence to support this.

    On the other hand, many medical professionals believe that there may be a link between graying and a constant state of anxiety or tension. Does stress cause gray hair? There is no scientific evidence to support the theory, but it is best to avoid stressful situations.

    Forest Schools originated in Sweden in the 1950s and spread to other countries, particularly Denmark where they have become an important part of the Danish early years program.

    In a typical Danish Forest School, young children from 3 years are taken into the forest for 4 hours each day of the week. They take no toys with them, but instead use only what the forest provides (and their imaginations) to develop their games. There is a primitive hut in the forest, which is used in extreme weather. Activities are child-led and fun, such as finding small animals or stomping in puddles. Because of high adult to child ratios, children can safely try out activities which are often considered too dangerous, such as climbing trees or lighting fires, and by dressing the children in good protective clothing, they are able to play freely. By setting children small manageable tasks at which they are unlikely to fail, and giving genuine praise, children's independence and confidence grow.

    A Swedish scientific study found that children in the Forest School are more balanced and socially capable, have fewer sick days, are more able to concentrate and have better co-ordination than the city nursery children. The primary reason appeared to be the greater opportunities to play in nature, so that children play for longer at a time, tending not to disturb each other as much as children in the city nursery. The study observed that where children were interrupted, they became irritable, their stress level rose, and their ability to concentrate fell.

    The study also showed that the Forest School children had 25 % fewer sick days than the city children. One reason for this is that the air is nearly always better outside than indoors. Outside a child is not so exposed to virus and bacteria and not so likely to be infected by other children. Another reason may be that, since stress has been shown to have a negative effect on the immune system, high stress levels may be weakening the city children. The Forest School children, on the other hand, are in a pleasant, natural, fun and less stressful environment.

    If a family member blames you for something you have done, it is important to be careful about how you defend yourself. It is not a good idea to use ways that cause hurt, even if they would help you make a valid point. If you can think of an instance where the other person has done exactly what they accuse you of, for example, it would not be good manners to throw it in their face. You should only bring it up if you don't have a choice. Then, you should make sure that you do it respectfully.

    Even if a family member intentionally goes against reasonable wishes you may have, you should understand that people see even the most fundamental things in very different ways. Remember that people are different. If you consider any noise after midnight to be intolerable, for example, others may see it is completely acceptable. It can take them a great deal of time to change their behavior for a demand that they do not understand.

    Think about the family conflicts that you are worried about now. Check to see if your parents had similar problems. People who grow up with parents who fight unfairly often repeat the same behavior. Consider changing the unfair habits that you grew up with.

    Understand that memories tend to change. In long-standing family disputes, all parties involved tend to have completely different recollections of the original problem.

    Families are a curious concept—while family members often feel nothing but annoyed for one another, they will also often be there for them if they should ever be in serious trouble. When you feel resentment for someone, think about how far you would go for them if they happened to be in trouble. It could help soften you. Think about how you care for the other person.