In many high schools, there are strict rules about using mobile phones. If your phone rings in class, for example, the teacher will be very angry.

    Every mobile phone has a ringtone (铃声). It tells you that someone is calling you. Now, there is a ringtone called "mosquitotone (蚊子铃声)". Using it, students can receive calls and text messages (短信) in class but the teacher will not realize what is happening. How?

    Mosquitotone has a special sound. Only children and teenagers can hear it. As we get older, we are unable to hear some sounds with high frequencies (频率). As a result, a child or teenager can hear the mosquitotone ringtone, but someone of 20 or older can't.

    But sometimes, people over 20 can hear the ringtone. One British student's phone uses mosquitotone. In class, the student's phone rang. The 22-year-old teacher looked at the student and became unhappy. "I heard that. You know the rule: no mobile phone in class."

    Not all the students are interested in mosquitotone. Jerry Jones, a high school student of 17, says, "Using mosquitotone too often is bad for our hearing. I may use it for pleasure, but not in class. It's unfair(不公平的) to the teachers!"

    What do parents think of mosquitotone? "I think it is perfect for places like movie theaters," says Connie Neeson, 44. "Think about it. You're watching a film and someone's mobile phone rings. Mosquitotone is good because many people don't hear it. However, it also has a bad influence（影响） on their study if students use it in class."

    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.

    Every school day, we use schoolbags to carry all of our things to school. They are a big part of our lives. But have you ever thought about the history of the schoolbag?

    In the Han Dynasty (汉朝), students in old-style private schools used bamboo boxes to carry books to school. People consider the bamboo boxes to be the earliest schoolbags. They were usually two or three layers (层) in the box. Kids put different things like books, brushes, ink stones (砚) and paper in the boxes.

    Hundreds of years later, people developed a new kind of schoolbag called the budai, or the "hip-pocket". The budai was lighter than the bamboo box. With the founding (成立) of the People's Republic of China, military rucksacks (军用帆布包) became popular. Many people carried them when they were in school. Ask your grandparents or parents about these bags. Maybe they can tell you about their experiences of carrying them when they were in school.

    A new style of schoolbags has appeared in recent years. Many of them have colorful and fashionable designs (时尚的设计) on them, such as pictures of cartoons or pop stars. And they are more comfortable to use. Some students pull wheeled bags filled with heavy textbooks and others carry backpacks.

    Schoolbags are still changing. Can you imagine what future schoolbags will be like?

    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.

    Cars make our lives more convenient. But they can also be a problem. For example, fossil fuel(化石燃料) cars mainly cause air pollution.

    To improve the environment, many countries are developing electric vehicles(EVs，电动车). Among them, China is' taking a leading role and has created the world's largest EV market.

    Last year, over 40 percent of the 753, 000 EVs sold in the world were sold in China, more than twice as large as the number sold in the United States.

    "Filling up a fossil fuel car with gas is more expensive than charging an electric car," said Wu Hao, who bought an electric car this year.

    However, there are still some problems. It can be hard to find charging piles and the cars can't go far before needing to be recharged.

    Some of these problems are being solved. In 2014, China had 31, 000 charging piles. Now China has the world's largest EV charging network, with more than 167，000 charging piles in total.

    Developing EVs is one of many efforts that China has made to cut down pressure on its environment after the government promised to stop increases in carbon dioxide emissions by 2030.

    "As China goes, so will the world's car industry," the Wall Street Journal said. China has taken a leading role in the world's electric vehicle industry.