Let's try doing the following experiment.

 What to do：

 Use string to hang a paper clip or other small object at about chest（胸部）level.

 Pick up a stick，such as a broom handle. Take three or four steps away from the paper clip.

Now close one eye and walk toward the paper clip. Try to touch it with the tip of the stick. If you miss，try again，still keeping one eye closed. Now try it with both eyes open and see if it's easier to do.

 How it works：

 In the experiment，you have to judge how far away the paper clip is. Your brain has several ways of doing this.

 One simple way depends on how much your eye has to focus（聚焦）itself. Using only one eye，most people will find it difficult to touch the paper clip on the first try，but the brain still gets some information about distance—though not much.

 Your brain can judge distance much better when you look at something with both eyes. In fact，your brain has more than one way to use both eyes in judging distance. For example，to see anything clearly，you have to make both of your eyes point at the object. When you look at a nearby object，your eyes turn inward. You can feel this happening if you look at the tip of your finger and move your finger toward your nose.

 Your brain gets information from the eyes about how much they are pointing toward each other. Using that information，the brain can tell how far away any object is，whether it is a basketball or a paper clip.

    A new App has been used in South Africa to benefit (有助于)the relationship between wildlife and humans.

    Roadwatch, created by the Endangered Wildlife Trust (EWT),is designed to let drivers   record any roadkill they see on the country's highways.

    It may seem like a strange idea, but EWT says that it could become the perfect platform for receiving important information. Information on where endangered species (物种）are living and the danger that they are under from traffic can help to inform decisions on conservation of matters (物质守恒）in the future.

    People can use the App through Facebook, WhatsApp, SMS and Linkedin to report the   species, location, time and date of the creature that has been seen on the road.

    Wendy Collinson field officer at EWT suggested that it could lead to more people taking care on the roads and paying more attention to animals that may be trying to cross the roads. One of the biggest problems is with reptiles (爬行动物）and snakes, which she believes people hit on purpose, as they are generally seen as scary. However, they are important to the health of ecosystems, just as all creatures are and also need to be protected.

    Emily Taylor from EWT said, “Roadkill simply hasn't been studied here. The road ecology and how many endangered species are being killed, is something we need to know more about. We want people to report as much as possible.”

    There have been some other Apps to use in relation to wildlife spotting in South Africa, but most of them are about animals that have not been knocked down, including those helping to collect information of where certain species have been seen, such as in parks.

    Alsten Chase has written a book about Yellowstone National Park. He is worried about the damage the fires can do to the park. He is also concerned(关心) about the park rules. These rules say that nature should decide what happens to the park. Alsten also writes that the elk herd(马鹿群) has grown too big. The elks walk on the riverbanks. They eat the new grass and roots of baby trees. The beavers(河狸) need the trees to build dams(坝).

    The dams raise the water levels. Higher water levels put more water into the soil. Wet soil helps plants grow faster. The plants offer homes and food to other animals.

    Chase thinks that the park rules would work only in a park with natural settings. He believes that Yellowstone has had an artificial(人为的) setting for a long time. The native people left. The wolves were taken away and other animals were removed. The areas of land were fenced off(隔开) and other animals added. He thinks the park rules that let herds grow too big and the fires are hurting the nature of the park.

    The park manager thinks the rules are good and that the park will be fine. Chase thinks the way the people run the park should be changed.

    The Earth is about 4, 600 million years old Man lives on the Earth for only 35, 000 years. But we change our Earth in many ways. Many things we do are good, but some are not good for the Earth.

    Water pollution

    A lot of people, birds and fish die each day because of water pollution. Factories pollute the water. As a result (因此), the water in many rivers and lakes is now very dirty.

    Air pollution

    In big cities, factories, cars and buses are the main causes of air pollution. Many people in cities now have health problems. For example, Mexico City used to be a beautiful sunny capital, but today there are many clouds in the sky. And many people get ill because of the polluted air.

    Soil (土壤) pollution

    In order to have a better harvest (收获), some of the farmers use chemicals too much in their fields. That's bad for the soil.

    Hope for the future

    These problems are very serious for our future, so all of us should do something to protect the environment. If we can stop pollution, our Earth will become more and more beautiful.