One day, Mr. Arnold was teaching a lesson, and things were going as normally as ever. He was explaining the story of human being to his pupils. He told them that, in the beginning, men were nomads (游牧); they never stayed in the same place for very long. Instead, they would travel about, here and there, in search of food, wherever it was to be found. And when the food ran out, they would move off somewhere else.

    He taught them about the invention of farming and keeping animals. This was an important discovery, because by learning to cultivate (耕作) the land, and care for animals, mankind would always have food steadily. It also meant that people could remain living in one place, and this made it easier to set about tasks that would take a long while to finish, like building towns, cities, and all that were in them. All the children were listening attracted by this story, until Lucy jumped up:

    "And if that was so important and improved everything so much, why are we nomads all over again, Mr. Arnold?"

    Mr. Arnold didn't know what to say. Lucy was a very clever girl. He knew that she lived with her parents in a house, so she must know that her family were not nomads; so what did she mean?

    "We have all become nomads again,” continued Lucy, " The other day, outside the city, they were cutting the forest down. A while ago a fisherman told me how they fish. It's the same with everyone: when there's no more forest left, the foresters go elsewhere, and when the fish run out, the fishermen move on. That's what the nomads did, isn't it?

    The teacher nodded, thoughtfully. Really, Lucy was right. Mankind had turned into nomads. Instead of looking after the land in a way that we could be sure it would keep supplying our needs, we kept developing it until the land was bare. And then off we would go to the next place! The class spent the rest of the afternoon talking about what they could do to show how to be more civilized (文明的).

    The next day everyone attended class wearing a green T-shirt, with a message that said "I am not a nomad!"

    And, from then on, they set about showing that indeed they were not. Every time they knew they needed something, they made sure that they would get it using care and control. If they needed wood or paper, they would make sure that they got the recycled kind. They ordered their fish from fish farms, making sure that the fish they received were not too young and too small. They only used animals that were well cared for, and brought up on farms.

    And so, from their little town, those children managed to give up being nomads again, just as prehistoric men had done, so many thousands of years ago.

    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)”.

    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 about 6.0-magnitude(震级) earthquake(地震) hit Yi'bin, Sichuan at 22:55 on June 17th, 2019,and it killed at least 12 people and injured(受伤的) more than 220.

    Many people in Chongqing felt it. Most of them rushed out to the safe places such as the square, the playground, the street .But some didn't.

    What can we do when an earthquake happens? In fact, there's little we can do to stop natural disasters(自然灾害) such as earthquakes happening. But, some methods can reduce(减少) the harm they cause.

    Drop down onto your hands and knees. This way can protect you from falling.

    Cover your head under a strong table or desk. You can also stay along a wall, and cover your head with your arms and hands.

    Hold on to(守住，抓牢) your shelter(遮蔽物) until the shaking stops. Be prepared to move with your shelter if the shaking continues.

Schools can normally take the earthquake drills(演练) to help student stay alive.

    RIVER DOLPHIN RUNNING OUT OF TIME

The Yangtze dolphin is the only kind of dolphin that lives in freshwater all its life. Scientists say that the finless freshwater dolphin that has lived in the Yangtze River for over 20 million years, will die out in 15 years. It's in danger of disappearing forever.

    Dangers:

    Dredging(挖掘) of their habitat

    Heavy boat traffic in the Yangtze River

    Insecticide(杀虫剂) and mercury(汞)

    A few years after World War Ⅱ finished, scientists spoke with great eagerness about the use of nuclear power as a source of energy. Within twenty years, they said, nuclear would take the place of coal, gas and oil as a source of power at home and in industry. This promise has never been carried out(兑现)and there are serious doubts that it ever will be. Nuclear power plants are used to produce energy in some wealthier countries, but the cost is high.

    Although safety measures have been taken, radiation leaks have taken place and workers have been killed or affected. The problem of getting rid of the nuclear waste has proved most difficult. There is a limit to the amount of waste materials which can be buried in the ground or poured on the sea-bed. These methods may also cause more problems. Waste materials polluted by radiation may remain dangerous for 200 years or more.

    It is no surprise that scientists have now turned to the sun and the sea as sources of power. The sun shines day after day almost wastefully, providing us with energy far be yond all our needs.