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.

    Pollution inside homes and other buildings kills more than 4 million people each year．Many people die as a result of breathing smoke or from cooking over wood﹣powered of coal﹣powered stoves．

    One way to reduce the number of deaths is through cooking equipment powered by the sun．Crosby Menzies，a solar power expert in a South African company，described his latest solar cooker called the“Sol.4”，”It is four square meters of mirrors，six to eight meters in length．It is quite a large cooler．”

    The“Sol.4”works by reflecting （反射）light from the sun off large mirrors．The mirrors direct （把…对准）the light at a cooking pan．Then the light heats the pan with solar energy．Within two minutes，the pan is hot enough to cook sausages and onions．In just four minutes，water can be boiled．That is as fast as cooking with natural gas or electricity．

    The cooker is also much“friendlier”than other models because people do not have to stand in the sun to use it．And people can prepare meals without having to collect firewood or spend money on coal．Suchindividualswould be less likely to have breathing illnesses from harmful smoke．

    At present，the cooker only works when the sun is shining．But engineers are working on a way to make it work without sunlight．

    Each cooker costs about $2000，which is a large amount of money for most Africans．To solve that problem，Crosby Menzies has crated a non﹣governmental organization called solar Cookers for Africa．It plans to raise money through donations to provide poor people with solar cooking equipment．

    You probably know a typhoon is a large and powerful storm that can cause a lot of rain and wind. Everyone pays attention to typhoons because they can be dangerous. Some typhoons come and go and really don't cause much more trouble than a bad thunderstorm. Others may damage homes and cause some floods that go away on their own.

    Typhoons are always a concern, especially for people who live near the coast. When a typhoon is on the way, weather forecasters can say which areas will be affected. Maybe you've heard people call a typhoon a "natural disaster", but what does that mean? A natural disaster is something that happens in nature and causes big problems, like a typhoon, a tornado(龙卷), an earthquake, or a tsunami. But wherever you live, it's important to remember that there are lots of people looking out for you. In a bad storm or other crisis, this would include not only mums and dads, but also police officers, firefighters, doctors, nurses, and other people who are trained to handle emergencies.

    Sheridan is a town in Indiana, USA. There are lots of trees near the public schools in the town. Their leaves turn sunlight into energy（能量）.

    In Sheridan, the sun not just provides energy for plants. It keeps schools running, too. The schools use solar panels（太阳能电池板） to turn sunlight into energy.

    The science behind solar energy is not new. But Sheridan Community Schools is the first school district(学区) in Indiana to be completely solar-powered. The district finished putting in solar panels for all three of its schools in 2016. Some of the panels can turn to follow the sun across the sky.

    In 2008, fewer than 1. 000 schools used solar power. By 2014, there were 3, 727 schools with solar panels in the USA. These numbers come from a report by the Solar Foundation. Roxie Brown, a program director there said that the number of schools with solar panels has continued to go up since 2014.

    Solar energy has some advantages over other energy sources(来源). Sunlight is a renewable source, which means it won't run out. Solar panels don't harm the environment. Also, sunlight is free. So by using solar power, schools can save money on energy costs.

    Brown thinks more schools should run on solar energy. "The sun is Earth s energy source," she says. "We're trying to make it the energy source for our houses cars and schools, too."

    But using solar energy isn't always easy. Solar panels can be expensive to put in. The panels also take up space. But for many schools, going solar is worth it.

    Would you like to go to the zoo at night? Last month, Shanghai Wild Animal Park opened its night safari(夜间观赏)for the first time. You can see animals in the dark. Some animals enjoy the night—they are nocturnal(夜行的)animals. Who are they?