Plants are very important living things. Life could not go on if there were no plants. This is because plants can make food from air, water and sunlight. Animals and men can't make food from air, water and sunlight. Animals get their food by eating plants and other animals. Therefore, animals and men need plants in order to live. This is the reason why we find so many plants around us.

    If you look carefully at the plants around you, you will find that there are many kinds of plants. Some plants are large while others are small. Most plants are green.

    Some plants have many small leaves. Others have only a few. There are many kinds of leaves. Leaves are of different shapes and colors.

    Leaves are also different in other ways. Some leaves have long thin parts at the end, we call them leaf stalks, some have short leaf stalks, others even have no leaf stalks. The leaf edges are also different. Some leaves have smooth(平滑) edges. Some have a wave-shaped edges. Others have edges like the teeth of a saw(锯子).

    Do you know some great inventors and their inventions?

    What factors (因素) are needed for their success?

    Well, good timing for a start. You can have a great idea which the public simply doesn't want … yet. The Italian Giovanni Caselli invented the first fax（传真）machine in the 1860s. Although the quality is excellent, his invention quickly died a commercial(商业的) death. It was not until the 1980s that the fax became very common in every office… too late for Giovanni Caselli.

    Money also helps. The Frenchman Denis Papin (1647-1712) had the idea for a steam engine （蒸汽机）almost a hundred years before the better-remembered Scotsman James Watt was even born… but he never had enough money to build one.

    You also need to be patient (it took scientists nearly eighty years to develop a light bulb which actually worked)… but not too patient. In the 1870s, Elisha Gray, a professional inventor from Chicago, developed plans for a telephone. Gray saw it as no more than “a beautiful toy”. However, when he finally sent details of his invention to the Patent Office(专利局) in February，1876, it was too late. Almost the same invention had arrived two hours earlier and the young man who sent it , Alexander Graham Bell, will always be remembered as the inventor of the telephone.

    Of course what you really need is a great idea—but if you haven't got one, a walk in the country and a careful look at nature can help. The Swiss scientist, George de Mestral, had the idea for Velcro(魔术贴) when he found his clothes covered in sticky seed pods after a walk in the country. During a similar walk in the French countryside some 250 years earlier, Rene Antoine Ferchault de Reaumur had the idea that paper could be made from wood when he found an abandoned wasps' nest(蜂巢).

    You also need good commercial sense. Willy Higinbotham was a scientist doing nuclear (核能的)research in the Brookhaven National Laboratory in Upton, USA. In 1958 the public were invited to an exhibition in the Laboratory to see their work, but both parents and children were more interested in a tiny 120cm screen with a white dot which could be hit back and forth over a “net” using a button and a knob. Soon hundreds of people were ignoring the other exhibits to play the first ever computer game—made from a simple laboratory instrument called an “oscilloscope”. Higinbotham, however, never made money from his invention: he thought people were only interested in the game because the other exhibits were so boring!

    Humans are going to the Moon for the first time since the last Apollo Mission( 飞行任务) in 1972, 45 years ago.

    SpaceX, a US space technology company, will send two people on a private trip around the moon. And they plan to make it happen in 2018, reported CBS News.

    The company didn't name the two people, how much they were paying or even their gender(性别). But they did say that the mission would use SpaceX's Falcon Heavy rocket and Dragon 2 spacecraft. Both of them are still in development(研发).

    The founder of the company Elon Musk mentioned that the trip would last about a week. "The plan is crazy." Mark Shelhamer, a former scientist from NASA said. "It's impossible to complete the mission. Getting to the moon is a lot more difficult than getting to the International Space Station." However, Musk believes that the trip will be a great success. The spacecraft will run on autopilot(自动驾驶) and the two space tourists will get hard training.

    "There is some risk there," Musk said. "But we'll do everything we can to minimize(将…减到最少) that risk."

    Skin-diving (自由潜水) is a new sport today. This sport takes you into a wonderful new world. It is like a visit to the moon! When you are under water, it is easy for you to climb big rocks because you are no longer heavy. Here, under water, everything is blue and green. During the day, there is enough light. When fish swim nearby (附近), you can catch them with your hands. When you have a tank (罐) of air on your back, you can stay in deep water for a long time. But you must be careful. To catch the fish is one of the most interesting parts of this sport. On the other hand, you can clean the ships without taking them out of the water. You can get many things from the deep sea. Now you can see that skin-diving is both useful and interesting.

    People and dogs have been living together for hundreds of years. When did dogs and people become friends? Where did dogs come from?

    A group of scientists tried to answer these questions. They just finished a study about the history of dogs. In the study, they looked at the DNA of dogs all over the world and found that dogs, like humans, shared DNA with their family members. The scientists put together a big family tree for dogs. It went all the way back to the animal's beginning.

    In this way, scientists learned about the history of dogs. The first dogs lived in Asia. They were born about 33,000 years ago. At first, there were only about 6,400 of them. Their parents were wolves(狼).

    The new study answers many questions. It raises some too. For example, what caused wolves in Asia to become dogs all those years ago?

    One idea is that their DNA slowly changed and the wolves became dogs in the end. As time goes by, dogs became "man's best friends" Or it could happen the other way around. It was possible that some wolves started living with people before they became dogs. Living with people led to many changes to these wolves. It changed their DNA, so their offspring(后代) became dogs. In other words, it was possible that wolves were our friends before they became dogs.

    By studying DNA, scientists now have a much better understanding of the history of dogs. ________.

    How exactly dogs came to be our friends is still unclear.