Are you able to send a letter with pictures and sounds to someone somewhere in the world without a stamp(邮票) on it? Using a computer you can send e-mails quickly and easily. The post is much slower than e-mail. E-mail can send its message to the other side of the world in seconds.

    E-mail is easy to use and it saves time and money. The differences in time in different parts of the world do not matter when sending e-mail. It's twenty-four-hour service(服务) that you can send e-mail at any time of the day or night. No one has to be there to get e-mail. It does not matter if your friends are in beds when you send e-mail to them, or you are seeing a movie at the movie theater when they send e-mail back.

    We know the mosquito very well. Mosquitoes fly everywhere. They can be found almost all over the world， and there are more than 2，500 kinds of them.

    No one likes the mosquito. But the mosquito may decide that she loves you. She？ Yes，she. It's true that male mosquito doesn't bite（咬） and only the female mosquito bites because she needs blood to lay eggs. She is always looking for things or people she wants to bite. If she likes what she finds， she bites. But if she doesn't like your blood，she will turn to someone else for more delicious blood. Next time a mosquito bites you，just remember you are chosen. You're different from the others！

    If the mosquito likes you，she lands on your body without letting you know. She bites you so quickly and quietly that you may not feel anything different. After she bites，you will have an itch（痒） on your body because she puts something from her mouth together with your blood. By the time the itching begins，and she has flown away.

    And then what happens？ Well，after her delicious dinner，the mosquito feels tired. She just wants to find a place to have a good rest. There，on a leaf or a wall， she begins to lay eggs，hundreds of eggs.

    Lasers（激光） have many uses including improving someone's eyesight, playing DVDs, cutting the diamonds（钻石） and the list goes on and on. Now, there could be a new use for this powerful tool-changing the weather!

    The Swiss scientist Jean Pierre Wolf is working on using laser beams（激光束） to change the weather for the better. He wants to use it to help stop climate（气候） change. Sounds crazy, right? Well, there is already something kind of like it.

    Cloud seeding（云催化） is a way people stop rain from falling. It uses rockets to release chemicals into the atmosphere（大气层）, but it's not known what this might do to the environment. So Professor Wolf wants to find a better way to do this, and a laser is a good choice since the only thing it uses is light, not chemicals. But how would it work? According to CNN, it would make new clouds. The laser would make condensation（冷凝） happen, in other words producing drops of water. And then the water would turn into really small pieces of ice. Then clouds start to be made just naturally.

    Professor Wolf's hope is to help control the weather in places like California that can face both heavy floods and droughts（干旱）.They are also trying to use lasers to control lightning. Using lasers to change the weather has been tested in a lab, and they have been quite successful in some fields. They are still trying to find out how to use it in the real world, but it could be a new way to stop climate change. "Every time you think you have done everything you can with lasers, something new comes up," said Professor Wolf. "It's quite amazing."

    Art, as we know, is subjective. What one person considers a priceless masterpiece others might see as nothing more than a giant black square. But there's one very specific kind of painting that almost everyone sees the same way-the kind with the" "strange" eyes that seem to follow you around the room. So what causes this optical illusion (视觉错觉) and how do artists achieve this effect?

    It turns out, for even a moderately skilled artist, this effect isn't a difficult thing to achieve, In fact, the artists need to use a little illusion of depth, making the person depicted on the canvas appears somewhat 3D on a 2D canvas, and to adjust .the gaze (凝视) of the eyes so that they would be looking at someone standing right in front of the picture.

    So what exactly is going on here in our brains that then makes it seem like the eyes follow you even if you move away from being front and center? As demonstrated by a team of researchers from Ohio State University, as you move to the side, the "near? and "far" points of the 2D image don't really change. These near and far points are defined as visible points that, if the image was 3D, would appear nearest and furthest away from the viewer at a given angle.

    The idea is simple. No matter what angle you look at a paining from, the painting itself doesn't change. You're looking at a flat surface. The key is that the near points and far points of the picture remained the same no matter the angle the picture was viewed from. When observing real surfaces in the natural environment the near and far points vary when we change viewing direction. When we observe a picture on the wall, the visual information that defines near and far points is unaffected by viewing direction. Still, we willingly accept and interpret the thing in the painting as if it were a real object.

    Thus, because the perspective, shadows, and light on the painting don't change as you move around, if the eyes in the painting would be staring directly at the observer who is standing in front of the painting, it creates something of an optical illusion in your brain so that the eyes will continue to seem to stare at you as you move to the side.

    In contrast to the eyes following you trick, if the artist tweaks the painting a bit, for example the artist adjusts the gaze of the eyes so that the eyes are looking off somewhere else instead of directly looking at a potential observer, no matter where you stand, the eyes will never seem to be looking at you.

    The technique first began popularly showing up in art around the 14th century when the artist and architect Fillipo Brunelleshi introduced the art world to the idea of "linear perspective", being painting with the idea of everything in the picture converging (聚集) on a specific point on the horizon, creating the illusion of depth. Linear perspective, combined with skilled use of light and shadow, allows artists to create masterfully realistic paintings, including sometimes of people that stare at you creepily no matter where you stand.

    How green are you？Do you know how to be green？

    We all need a healthy environment, but we produce waste every day and it does harm to our environment. Though we are young, we can still do something to help. In fact, even the simplest everyday activities can make a real difference to the environment. Here are some ideas for you.

    Reduce

    Reduce means" use less". Don't waste things. This saves money and reduces pollution and waste going into the environment. Before we buy something new, think whether it is really necessary﹣or maybe the old one will be just as good! When we do buy things, choose local products if possible, and try not to buy too many things from abroad.

    Reuse

    Reuse means" use again". Use things for as long as possible. When we buy things, make sure that they last a long time. We should look after them so that they will last, and we should repair them if we can instead of throwing them away and buying new ones. Don't use a paper cup of a paper bag. It's better to use a china cup and a lunch box because you can use them again.

    Recycle

    Recycle means" change things into something else". Though it takes energy to change something into something else, it's better than throwing things away or burning them. Find out what can be recycled in your neighborhood and take part in recycling programmes. We should also buy products made from recycled materials, such as recycled paper, to help save trees.

    So please remember these three words: reduce, reuse and recycle.