As space science develops, man has learned more and more about space. Space is not only amazing but also dangerous. While working in space, spacemen are facing danger as well as success.

    Scientists have found out that the radiation（辐射）is the greatest danger to spacemen in space. When spacemen are working in space, they are in danger of the radiation from the sun and other stars, which is bad for their health. The harm of the radiation won't be found until their children even grandchildren are born. Some special medicine may work a little, but no really effective medicine has been found so far.

    Space rubbish is also thought to be a great danger to spacemen. It's reported that there were 9,000 man-made things flying in space. About 30% of these are satellites, 10% are spaceships, and the rest are space rubbish. An explosion（爆炸）in space in 1999 made a cloud of 300,000 fragments, each at least 4mm in size. A small piece of these even knocked a spaceship window and caused some damage（损坏）.

    Scientists are watching and reporting any possible danger all the time. They are working to deal with space rubbish. Although space is really dangerous, it interests many people on the earth. In the near future, it may be possible for people to spend a few days in a space hotel. We may even choose to leave the earth and live in space in a few years. So we should do something to help improve the space environment.

Would it surprise you to learn that, like animals, trees can communicate with each other and pass on their wealth to the next generation—their young trees?

    Suzanne Simard, forest ecologist(生态学家) at the University of British Columbia, explains how trees are much more complex(复杂的) than most of us ever imagined. Although Charles Darwin(达尔文) thought that trees are competing for survival of the fittest, Simard and her team have made a new discovery and showed just how wrong he was. In fact, the opposite is true: trees survive through their group work and support, passing around necessary nutrition(营养) such as nitrogen(氮) and carbon "depending on who needs it".

    Nitrogen(氮) and carbon are shared through miles of underground fungi (真菌) networks. This makes sure that all trees in the forest ecological system give and receive just the right amount to keep them all healthy. This system works in a very similar way to the networks of neurons (神经元) in our brains, and when one tree is destroyed, it influences all.

    Simard talks about "Mother trees". These are usually the largest, oldest plants that on which all other trees depend. These "Mother trees" are connected to all the other trees in the forest by this network of fungi, and may manage the resources of the whole trees and plants in the forest. She explains how these trees pass on the wealth to the next generation, transporting important resources to young trees so they may continue to grow. When humans cut down "Mother trees" without paying attention to these highly complex "tree societies" of the networks on which they feed, we are reducing the chances to save the whole forest.

    "We didn't take any notice of it," Simard says sadly. "Mother trees" move nutrition into the young trees before dying, but we never give them chance. If we could put across the message to the forestry industry, we could make a huge difference towards our environmental protection efforts for the future.

    What is the best way to help control air pollution in our towns and cities? Choose public transportation instead of private cars, or reduce the total amount of cars on the street. These can be useful. But here is a more creative way—write a poem.

    "I write in praise of air. I was six or five, when a magician opened my fist(拳头), and I held in my hand the whole of the sky."

    Professor Tony Ryan (the science expert) and Professor Simon Armitage(the words expert), from the University of Sheffield, UK, came up with the idea.

    But in fact, the poem is not the key part. It is the poster that the poem was written on that plays the biggest part. The poster is 10 meters by 20 meters. It is coated with nanoparticles(纳米粒) of titanium dioxide (二氧化钛). It can absorb the waste from around 20 cars each day if you put it by a busy road. The poster is now displayed on one of the University of Sheffield's buildings.

    It doesn't get rid of all the pollutants from traffic, but it will eat up things called nitrogen oxides (氧化氮). These play a part in breathing problems, including asthma(哮喘).

    The technology is cheap. "It would add less than £100 to the cost of a poster and would turn advertisements into catalysts(催化剂) in more ways than one," Ryan told the BBC.

    He's also working on another idea, which is to add the nanoparticles to washing powder, so that your clothes soak up these poisons while you walk along. And you wouldn't be able to see or feel anything different.

    We can see walls everywhere in the world. But the Great Wall of China is the biggest of all. The Chinese call it "The Ten-Thousand-Li Great Wall". It is in fact more than 6000 kilometers long. It is 6～7 meters high and 4～5 meters wide. In most places, five horses or ten men can walk side by side along the top.

    When you visit the Great Wall, you can't help wondering how the Chinese people were able to build such a great wall thousands of years ago. Without any modern machines, it was really very difficult to build it. They had to do all the work by hand. It took millions of men hundreds of years to build it.

    The Great Wall has a history of over two thousand years. The men began to build the first parts of it around two thousand seven hundred years ago. Then QinShihuang had all the walls joined up. He thought that it could keep the enemy out of the country.

    Today the Great Wall has become a place of interest. Not only Chinese people but also people from all over the world come to visit it.