Nearly all our food comes from the soil. Some of us eat meat, of course, but animals live on plants. If there were no plants, we would have no animals and no meat. So the soil is very necessary for life. The top of the ground is usually covered with grass or other plants. There may be dead leaves and dead plants on the grass. The waste matter(粪) from animals also falls on it.

    All soil needs food. If we do not give it any, the plants will be weak. Farmers found that animals' waste is the best food for the soil, but chemical fertilizers(化肥) are also very useful. The same crop（庄稼）should not be grown in the same place every year; it 's better to have a different crop. A change of crop and the use of a good fertilizer will keep the land good.

    Not many years ago, some farmers were worried because hawks ( 鹰) were taking many of their chicken. The farmers didn't know what to do. Finally they went to the country officials and asked for help.

    "Kill the hawks," the officials said. "We will even pay for them." So the farmers began to think of ways to kill the hawks.

    The farmers killed many hawks. They no longer had to worry about their chickens. But they now had a new worry. Field mice were eating up a lot of the farmers' grain.

    How did this happen?

    Hawks cannot only chickens but also field mice. They eat more field mice than chickens. But the farmers didn't know this. When they killed a lot of hawks, they changed the balance.

    When people move into a new place, they often destroy many wild plants. Often these plants are food for the animals. If the animals can't find enough plants to eat, they will starve or have to leave the place.

    In one part of the USA, for example, the deer there like to eat a certain kind of wild roses. The mountain lions there eat the deer. The number of deer, mountain lions and wild roses doesn't change much if people leave things as they are. But people killed many mountain lions in order to protect the deer. Soon there were so many deer that they ate up all the wild roses. Then the deer began to eat the green leaves of young trees. These trees were important to the farmers. So the farmers thought of ways to protect their trees. Now the deer had nothing to eat, and many of them died. This was another lesson from nature.

    To keep the balance of nature is important for us to remember.

    Do you know the whales in the sea? There are many relatives(亲属) in the whale family and they always live together with whales.

    Few people know dolphins(海豚) are part of the whale family. Dolphins are not fish. They are mammals(哺乳动物). They breathe air, and they have babies and feed them with milk. Dolphins are famous for their wonderful shows. They can jump high out of the water and show turns in the air. These jumps give the dolphins time to breathe.

    Porpoises(鼠海豚) are also in the whale family and are quite like dolphins. But they are different in the size and shape of the mouth. The dolphin's mouth is long and thin, but the porpoise's is short and thick. Dolphins are also more talkative than porpoises. Dolphins make sounds to talk with each other under water. But porpoises do not do this. Both of them are smart and friendly to humans.

    Not all the members of the whale family are friendly. Big whales are much easier to be angry than smaller dolphins or porpoises. An angry whale can be dangerous. Perhaps this helped to create the story of Moby Dick that sank (使下沉) a ship and made all the people on it die in the sea.

    How do you pay for your meals at a fast food restaurant? With change(零钱)? Nowadays we have We Chat wallet and Alipay.

    I use my tap-and-go card(感应式信用卡). I don't even need to enter my PIN number(SIM卡密码)or a signature(签名)to pay money. It's quicker and everybody in the queue(队)is happy.

    Contactless payments(非接触式支付)are more and more popular, but the safety (安全性)still needs improving(改善). And people shouldn't pay too much at a time-in the UK it's ￡30. If you use the card a few times, you will need your PIN number.

    Some things, such as your clothes, have been combined with electric technology(与电子技术联系起来). Kenneth Cukier, the writer of the book Big Data, says, "You can take any card and put it in a coat. When you make a payment, just wave your arm in front of the terminal(终端)." This is for people who don't want to take their card out of their pocket, or use their phone or watch.

    Good, isn't it?

    So spending money is becoming easier at the time. And people are buying more and more things. But making money still needs the hard work.

    Back to work then!

    Get a lot of letters at this time of year from people complaining (抱怨) that they have a cold and that it won't go away. There are so many ways to cure (治愈) a child. It is often difficult to know what to do. Although (尽管) cold are rarely (很少) dangerous, weak people , such as the elderly or young babies, often catch them. Colds are always uncomfortable and sometimes very unpleasant. Of course, you can buy lots of medicine. This will help to make your cold less unpleasant, but you must remember that nothing can actually cure a cold or make it go away quickly.

    Another thing is that any medicine can be dangerous if you are already taking another type of medicine for some other illness. So always check with your chemist (药剂师) or doctor to see if they are all right for you. Also, remember that they might make you sleepy; please don't try to drive it they do! Lastly, if you want to keep away from colds, don't blindly (盲目地) believe in 'magic' foods or drinks. The best way is to keep strong and healthy –you'll have less chance of catching a cold, and if you do, it shouldn't be so bad!