While we all try to find happiness, sometimes we still end up feeling low. While most people can control this feeling, low moods can stay with some, leading to depression. About 322 million people suffered from depression in 2015, according to a report by the World Health Organization in February. This is more than 4 percent of the world's population.

    Depression is described by the WHO as a mental disorder. It has several symptoms including sadness, loss of interest and feelings of low self-worth. In severe cases, depression may even lead to suicide.

    The number of people living with depression is increasing. The WHO reported a rise of 18.4 percent between 2005 and 2015. Young people are a group known to suffer with depression. “The pressures on today's youth are like no other generation, perhaps,” Dan Chisholm, an official of WHO, told Reuters.

    In China, depression among young people is on the rise, Zhu Zhuohong, a psychology professor with the Chinese Academy of Sciences, told Xinhua News Agency. Competition to outperform others, especially in education, can cause a lot of pressure for Chinese youth.

    Almost 1.2 million Chinese people aged 15 to 24 suffer from depression, according to a report released by British science journal The Lancet in May.

    Luckily, more and more efforts are being made to deal with this problem. This year's World Health Day, held on April 7, will focus on depression. The day will highlight (强调) the “Depression: let's talk” campaign. The campaign aims to make sure that people with depression both seek and get help.

    The Children's Book-Show Competition is a chance for young readers to be writers.

    Reading, it seems, is coming back in fashion, if a survey by the famous National Literacy Trust (the NLT) is true. It shows that the percentage of children who admit enjoying reading has grown for the first time in the past 8 years.

    So it's a good time to launch a competition that includes a shed-load of new books for schools as prizes. The Children's Book-show Competition, backed by The Independent, is taking to the roads again from the start of next term, with a nation-wide tour of 15 big cities, featuring a line-up of a dozen children's writers and illustrators (插图画家) aiming to persuade pupils to follow their footsteps.

    The competition, launched by the children's writer and illustrator Jessica Souhami, has two categories: the under-nine's and nine to 13-year-olds.

    Children are asked to choose their favorite fairy or folk tale and set it in an extraordinary place.

    Then they are to retell it with the aid of drawings and writings—whether it is set at sea, on a distant planet, in the future or in the past. The closing date for the competition is 30th November.

    “Tell your tale in pictures and in words, ”say the organizers of the competition. “It can be in a picture book or comic-book format.”

    The winner of each competition will receive a signed copy of a book by each of the 12 authors involved in this year's tour, plus £150 worth of books for their school. The runners-up will receive a signed copy of Souhami's new book.

    I receive many letters from children and can't answer them all – there wouldn't be enough time in a day. I'll try to answer some of the questions that are commonly asked.

    Where did I get the idea for Stuart Little and for Charlotte's Web? Well, many years ago, I went to bed one night in a railway sleeping car, and during the night I dreamed about a tiny boy who acted rather like a mouse. That's how the story of Stuart Little got started.

    As for Charlotte's Web, I like animals and my farm is very pleasant place to be – at all hours. One day, when I was on my way to feed the pig, I began feeling sorry for the pig because, like most pigs, he was going to die. This made me sad. So I started thinking of ways to save his life. Three years after I started writing it, it was published. (I am not a fast worker, as you can see.)

    Sometimes I'm asked when I started to write, and what made me want to write. I started early – as soon as I could spell. Children often find pleasure through trying to set their thoughts down on paper, either in words or in pictures. I was not good at drawing, so I used words instead. As I grew older, I found that writing could be a way of earning a living.

    Well, here is the answer to the last question. No, they are imaginary (虚构的) tales. In real life, a family doesn't have a child who looks like a mouse and a spider doesn't write words in her web. Although my stories are imaginary, I like to think that there is some truth in them, too – truth about the way people and animals feel, think and act.

    Imagine you went to a restaurant with a date, had a burger, paid with a credit card, and left. The next time you go there, the waiter or waitress, armed with your profile data, greets you with, "Hey Joe, how are you? Mary is over there in the seat you sat in last time. Would you like to join her for dinner again?" Then you find out that your burger has been cooked and your drink is on the table. Forget the fact that you are with another date and are on a diet that doesn't include burgers. Sound a little odd? To some, it is the same with the Internet. The Nets ability to profile you through your visits to and interactions at websites provides marketers with an enormous amount of data on you--some of which you may not want them to have.

    Are you aware that almost every time you access a website you get a "cookie"? Unfortunately, it's not the Mrs.

    Reid's type. A cookie on the Internet is a computer code sent by the site to your computer--usually without your knowledge. During the entire period of time that you are at the site, the cookie is collecting information about your interaction, including where you visit, how long you stay there. How frequently you return to certain pages, and even your electronic address. Fill out a survey to collect free information or samples, and marketers know even more about you--like your name, address, and any other information you provide. While this may sound scary enough, cookies aren't even the latest in technology. A new system called I-librarian Alexa--named for the legendary third century.

    B. C. library in Alexandria, Egypt--does even more. While cookies track what you are doing at one site, Alexa collects data on all your Web activity, such as which sites you visit next, how long you stay there, whether you click on ads, etc. All this information is available to marketers, who use it to market more effectively to you. Not only do you not get paid for providing the information, you probably don't even know that you are giving it.

    In ancient Egypt, a shopkeeper discovered that he could attract customers to his shop simply by making changes to its environment. Modern businesses have been following his lead, with more tactics(策略).

    One tactic involves where to display the goods. For example, stores place fruits and vegetables in the first section. They know that customers who buy the healthy food first will feel happy so that they will buy more junk food later in their trip. In department stores, the women's shoe section is generally next to the women's makeup section: while the shop assistant is going back to find the right size shoe, bored customers are likely to wander over and find some cosmetics they might want to try later.

    Besides, businesses seek to appeal to customers' senses. Stores notice that the smell of baked goods encourages shopping, so they make their own bread each morning and then fan the bread smell into the store throughout the day. Music sells goods, too. Researchers in Britain found that when French music was played, sales of French wines went up.

    When it comes to the selling of houses, businesses also use highly rewarding tactics. They find that customers make decisions in the first few seconds upon walking in the door, and turn it into a business opportunity. A California builder designed the structure of its houses smartly. When entering the house, the customer would see the Pacific Ocean through the windows, and then the pool through an open stairway leading to the lower level. The instant view of water on both levels helped sell these $10 million houses.

Earthworms don't move fast. But humans can accelerate the worms' spread. Fishermen often use invasive(蔓延性的) earthworms to catch fish. Many have introduced invasive earthworms to rivers, streams and lakes previously unexposed to these animals. Gardeners who use earthworms to make their soil rich may unknowingly introduce invasive ones. The worms even give rides in the mud on wheels, potted plants and road materials shipped around the nation.

But they're not everywhere yet. In the Great Lakes region, "20 percent of the land is earthworm-free," says Cindy Hale, a research biologist. Of the remaining 80 percent of land, half of the land has fewer than two earthworm species-meaning there isn't yet too much impact on the ecosystem, she explains. For these regions, she says, now is the time to take action. According to Hale, educating the public, especially fishermen, is one approach to stopping the spread of invasive earthworms. Identifying which lands are currently earthworm-free is another.

Ryan Huefimeier, a program coordinator for Great Lakes Wom Watch, has been working on a model that will help create large maps of areas with minimal(最小的) or no damage from earthworms. Ultimately, landowners can use it to identify earthworm activity on their property. once identified, lands with minimal or no earthworm damage should be protected.

But scientists suspect that once invasive earthworms arrive they can't be removed. And even if all could be, affected forests might never return to the way they were. "It's very much a story of learning to live with them," concludes Lee Frelich of the University of Minnesota's Center for Forest Ecology.

Forest ecologists have called earthworms "ecosystem engineers" because they can change or create habitats that otherwise would not be present. Whether this is a good thing depends on the situation.

"What the earthworms do and how we value it is what really matters." said Hale. "In one place-farm fields or gardens-we really like European earthworms and what they do, so we consider them good. In native hardwood forests, we really don't like what they do-so we consider them bad. You really have to understand how an organism(微生物) affects an ecosystem. Things aren't black and white."