Most of the flowers in nature are red, orange and yellow. If we have seen a black flower, it's chance in a million.

    People have made a survey to colors of more than four thousand kinds of flowers and discovered that only eight of them are black.

    As we know, sunlight is formed by seven colored lights. The wavelength of each light is also different, so the quantity(量) of heat in each light is also different. Flowers, especially their petals(花瓣), are easy to be harmed by high temperature.

    Black flowers can take in the light of all the wavelengths that make them dry up because of high temperature, so black flowers can hardly resist(抵抗) sunlight. But red, orange and yellow flowers can protect themselves from sunlight by reflecting(反射) the red light, orange light and yellow light, each of which has a large quantity of heat.

    Have you ever heard someone use the phrase "once in a blue moon"? People use this expression to describe something that they do not do very often. For example, someone might say that he tries to keep away from sweets because they are unhealthy, but will eat chocolate once in a blue moon. Or someone who does not like to. Go to the beach might say, "I visit the shore(岸边) once in a blue moon." While many people use this phrase, not everyone knows the meaning behind it.

    The first thing to know is that the moon itself is never actually blue.  This is just an expression. The phrase "blue moon" actually has to do with the shape of the moon, not the color.

    As the moon travels around the earth, it appears to change shape. We have certain names for certain shapes of the moon. For example, when we can see a small part of the moon, it is called a crescent moon. A crescent is a shape that looks like the tip of a fingernail(指甲). When we can see the moon appear in the sky as a thin crescent, it is called a new moon. When we can see the whole moon, it is called a full moon. Usually, there is only one full moon every month. Sometimes, however, there will be two full moons in one month. When this happens, the second full moon is called a "blue moon".

    It's predicted(预言) that there will only be 15 blue moons over the next 20 years. As you can see, a blue moon is a very unusual event. This fact has led people to use the expression "once in blue moon" to describe other" very unusual events in their lives.

    Today there are robots working in factories. Some can help to build cars, and they do easy jobs over and over again. Few people will do such jobs in the future because they are boring, but robots will never get bored.

    Scientists are now trying to make robots look like people. Some robots in Japan can walk and dance. However, some scientists believe that it will be difficult to make them really think like people. For example, scientist James White thinks that robots will never be able to wake up and know where they are. But many scientists don't think so. They think that robots will even be able to talk in 25 to 50 years.

    Some scientists believe that there will be more robots in the future. These new robots will look very different. Some will look like people, and others might look like animals. In India, for example, scientists made robots that look like snakes. When buildings fall down with people inside, these snake robots can help look for people under the buildings. This was not possible 20 years ago, but computers and rockets also seemed impossible 100 years ago. We never know what will happen in the future!

    DNA is the whole" map" of the human body. It is something that all humans have, and it tells the body what to do. DNA is the reason that we look like our parents, because we get some of their DNA to make our own.

    People have been trying to understand the human body for a long time. In 1860, Mr. Mendel discovered why we look the same as other people in our family. It is because of small things called "genes" (基因)in our body. In 1953, two scientists, Watson and Crick, found out that genes are really messages. They're written in the DNA with a special language.

    In 1961, another two scientists found the first" word" that they could understand in that language. It shows how DNA tells the cell(细胞)to build its parts. So far, scientists have found all the words in the DNA map, but we still don't understand what they all do. By understanding what just one" word" means, we can help to save people from several illnesses. So the more we understand, the more doctors will be able to do.

    Most people hope that this can help to make better medicine to help sick people. Other people worry that when we learn more" word" and find out more information, we will use it in the wrong way. Just to make people more attractive, or stop sick people getting jobs.

    We all want to protect the environment, but we're mostly too busy or too lazy to put up big change. There is nothing new here but if you follow at least some of these tips, you can be proud of yourself in the protection of the environment.

    Use LED light bulbs: They last much longer and they can save energy.

    Donate: You have many clothes or things you want to throw. If they are still usable, give them to someone who needs them.

    Turn off your devices: When you do not use a house device, turn it off. For example, if you don't watch TV, turn it off. Turn off the light when you leave a room.

    Walk or cycle: Driving is one of the biggest causes of pollution. If you want to use your car, ask yourself the following question: do I really need my car? Walk or use your bike if the journey is a short one.

    Detergent (洗漆剂):Use less dose of detergent to wash your clothes or dishes.

    Leaky faucets(漏水龙头):Fix them, or they will waste a lot of water.

    Rainwater: Think of collecting rainwater. This water can be used for different purposes.

    All these tips will help you save money and protect the environment.

    What's a spacewalk? Any time an astronaut gets out of a spacecraft(航天器) while in space, it is called a spacewalk. Astronauts go on spacewalks for many reasons. For example, experiments can be placed on the outside of a spacecraft. This lets scientists learn how being in space affects(影响) different things. By going on spacewalks, astronauts can also fix things instead of bringing them back to the earth to fix.

    When astronauts go on spacewalks, they wear spacesuits to keep themselves safe. Inside spacesuits, astronauts have the oxygen(氧气) they need to breathe and the water they need to drink. To keep the astronauts and the spacecraft safe, the astronauts must leave and go back to the spacecraft through a special door. When on a spacewalk, astronauts use safety  tethers to stay close to their spacecraft. Tethers are like ropes, connect the spacewalkers with the spacecraft. They keep astronauts from floating(漂浮) away into space. Another way astronauts stay safe during spacewalks is by wearing a SAFER. SAFER is worn like a backpack. It helps an astronaut move around in space.

    How do astronauts train for spacewalks? One way is by going for a swim. Floating in space is a lot like floating in water. Astronauts practice spacewalks underwater in a huge special swimming pool. For every one hour they will spend on a spacewalk, astronauts need to train seven hours in the pool. Another way astronauts practice for a spacewalk is by using virtual reality(虚拟现实). It looks and feels just like a spacewalk.

    Today, only three countries have finished spacewalks independently. They are Russia, the United States and China. The first person to go on a spacewalk in the world was Alexei Leonov from Russia. Zhai Zhigang is the first Chinese astronaut to go on a spacewalk. The world record of spacewalks is held by Russian astronaut Anatoly Solovyev. He has been on 16 spacewalks and spent more than 82 hours outside in space.