Imagine a perfect day: the weather is good and everything seems fine. When, suddenly, your mobile phone loses its signal, the television has no programs, and you can't get online with your computer.

    What has happened? These are just the types of problems a solar storm(太阳风暴) might cause. You may not think of storms as putting our society in danger. But today, a solar storm is as serious as other bad events, such as earthquakes.

    A solar storm is caused by solar flares (太阳耀斑) :large explosions (爆炸) near the sun that can give off lots of energy. The strong energy can stop the satellite systems (卫星系统) that control our computers, telecom networks and so on. These storms can even cause the power to go out for weeks or months.

    In the past few months, scientists have recorded some of the strongest sun flares in years. The most recent one happened around Valentine's Day, 2011. It caused radio and satellite signals to go down in some northern cities in China.

    "Solar flare activity is going to be much worse than what we've seen in the past. We're not talking about a few cities losing power, it could be half of the country, maybe more," SolarStorm Warning.com, a US website about space weather, warned.

    Scientists say that little can be done to predict such a storm. Governments around the world are trying to work together before the next storm, although they are not sure when that may happen.

    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.

Dear sir,

    I am doing a project(课题) at school about animals in danger. I think the situation all over the world is really terrible.

    Firstly, I feel so sorry for the giant panda. Pandas mainly live on bamboo. A panda can eat about half its body's weight(重量) of bamboo in 24 hours！That's a lot of bamboo. I think we should try to do more to stop cutting down their forests. We would be so sad if they disappear.

    Secondly, what we should try to protect more is the Chinese alligators(短吻鳄) . They live in some parts of eastern China. They live in freshwater rivers and lakes but the water in some places isn't clean enough for them to live in. It's really dirty in fact. The government should stop factories from polluting the lakes and rivers.

    If we protect these beautiful animals in China, more people may come to China to visit our beautiful country, especially to see the quieter areas in the country. Now most visitors just see the cities.

    I hope you will encourage(鼓励) more people to think about such an important subject.

Yours,

Huang Jing

    When the Audet family turns on the lights at Blue Farm, they are using electricity that comes from cows- cow manure(粪肥).

    Cows produce a lot of waste. One cow can create 30 gallons of waste each day. Now imagine the output of over 1,000 cows at Blue Farm. That's really a big amount.

    When farmers clean their barns, they put the waste together，and spread some of it on their fields for fertilizer(肥料). But now places like Blue Farm have a new way of using cow waste. They use it to produce electricity.

    Here's how it works: A big machine moves back and forth cleaning the barn floor. "The cows are animals of habit; they get used to it,and just lift one foot and then another to let it go by. "says Marie Audet.

    The machine pushes the manure into a big 600-gallon tank like a small swimming pool. The tank is called a digester(化粪池) because what happens there is just like what happens inside a cow: Bacteria(细菌) get to work and continue to digest the manure.

    Methane gas(甲烷;沼气) in the atmosphere is known as a "greenhouse" gas because it keeps heat just like a greenhouse does, causing our planet to warm up. That's an environmental concern. But the digester has a good result. Its gas is kept and used to power electric generators(发电机).

    At Blue Farm, the generators make enough electricity to power 400 homes. The Audet family sells the extra electricity they can't use themselves.

    Most teens need more than 9 hours of sleep each night. But about 1 in 4 teens has trouble in sleeping. Lack of sleep can affect everything from our feelings to how well we focus on tasks like studying. It can also influence sports performance, increase our chances of getting sick, and may lead to weight gain in some people.

    How can we get the sleep we need? Here are some ideas:

    Be active during the day. Get at least 60 minutes of exercise a day. Physical activity can decrease stress and help people feel more relaxed. Just don't work too close to bedtime because exercise can wake you up before it slows you down.

    Say goodnight to electronics. Experts suggest using the bedroom for sleep only. At least shut everything down an hour or more before lights out.

    Keep a sleep routine. Going to bed at the same time every night helps the body expect sleep. Creating a bedtime routine can improve this relaxation effect. Reading, listening to music, spending time with a pet, writing a diary or doing anything else can relax you.

    Expect a good night's sleep. Instead of worrying that you won't sleep, remind yourself that you can. Say "Tonight, I will sleep well." several times during the day. It can also help to practise breathing exercises or gentle exercises before bed.

    Everyone has a sleepless night once in a while. But if you regularly have trouble in sleeping and you think it's affecting your mood or performance, talk to your doctor.