In colonies (群体) that range in size from a few hundred to tens of millions, they organize their lives with a clear division of labor. Even more amazing is how they achievethis level of organization. Where we use sound and sight to communicate, ants dependprimarily on pheromone (外激素), chemicals sent out by individuals and smelled or tastedby fellow members of their colony. When an ant finds food, it produces a pheromone that will lead others straight to where the food is. When an individual ant comes under attack or is dying, it sends out an alarm pheromone to warn the colony to prepare for a conflict as a defense unit.

         In fact, when it comes to the art of war, ants have no equal. They are completely fearless and will readily take on a creature much larger than themselves, attacking in large groups and overcoming their target. Such is their devotion to the common good of the colony that not only soldier ants but also worker ants will sacrifice their lives to help defeat an enemy.

         Behaving in this selfless and devoted manner, these little creatures have survived on Earth, for more than 140 million years, far longer than dinosaurs. Because they think as one, they have a collective (集体的) intelligence greater than you would expect from itsindividual parts.

    Many teenagers feel that the most important people in their lives are their friends．They believe that their family members, especially their parents, don't know them as well their friends do．In large families, it is often for brothers and sisters to fight with each other and then they can only go to their friends for advice．It is very important for teenagers to have one good friend or many friends．Even when they are not with their friends, they usually spend a lot of time talking among themselves on the phone．This communication is very important in children's growing up, because friend can discuss something difficult to say to their family members.

    However, parents often try to choose their children's friends for them．Some parents may even stop their children from meeting their good friends．The question of “choice” is an interesting one．Have you ever thought of the following questions?

    Who choose your friends?

    Do you choose your friends or your friends choose you?

    Have you got a good friend your parent don't like?

    With this list, go to travel now!

    Northern Vietnam

    Vietnam is known as a cheap place to travel around, but Hanoi, the north area, often gets ignored by travelers. This is truly a shame, because Northern Vietnam is where the most wonderful scenery and culture can be found. Rice fields, high mountains, winding roads and friendly people are also found there.

   Bishkek, Kyrgyzstan

    With 93 percent of the nation covered in mountains and a rich history and culture that goes back to thousands of years, Kyrgyzstan is one of the most wonderful countries in the world. The capital city, Bishkek, is an unbelievable center for exploring Central Asia, with Silk Road remnants(残余部分)like the Burana Tower just a short drive away.

    Lisbon Portugal

    Lisbon offers a good mix of museums, historic buildings, electric music and nightlife, and squares and cafes. You will fall in love with this city when you visit it. It is much less expensive than many other European travelling places, so travelers can afford it

    Seoul, South Korea

    Seoul is an attractive place filled with high-tech, modern and historic buildings, delicious Korean food all at bottom prices. Plus, since Seoul is a major city, it is easy to get to it.

Dear Reader,

    Today I am going to ask you to support Wikipedia with a donation.

    Wikipedia is built differently from almost every other top 50 websites. We have a small number of paid staff，just twenty­three. Wikipedia content is free to use by anyone for any purpose. Our annual expenses are less than six million dollars. Wikipedia is run by the non­profit Wikimedia Foundation, which I founded in 2003.

    Wikipedia is driven by a global community of more than 150,000 volunteers — all devoted to sharing knowledge freely. Over almost eight years, these volunteers have contributed more than 11 million articles in 265 languages. More than 275 million people come to our website every month to access information,free of charge and free of advertising.

    But Wikipedia is more than a website. We share a common cause: Imagine a world in which every single person on the planet is given free access to the sum of all human knowledge. That's our commitment.

    Your donation helps us in several ways. Most importantly, you will help us cover the increasing cost of managing global traffic to one of the most popular websites on the Internet. Funds also help us improve the software that runs Wikipedia — making it easier to search, easier to read, and easier to write for. We are committed to increasing the free knowledge movement worldwide, by taking on new volunteers, and building strategic partnerships with institutions of culture and learning.

    Wikipedia is different. It's the largest encyclopedia (百科全书) in history, written by volunteers. Like a national park or a school, we don't believe advertising should have a place in Wikipedia. We want to keep it free and strong, but we need the support of thousands of people like you.

    Thank you,

Jimmy Wales

    From the loss of wildlife to rising sea levels, we're all well aware of the problems that climate change could cause.

    But while it may seem like such issues won't affect most of us directly，it looks like future generations could grow up without something that many of us now take for granted: chocolate.

    According to an essay published by the US National Oceanic and Atmospheric Administration, changes to the climate in the regions that produce cacao - the plant from which chocolate is produced - may mean that it will soon become extinct.

    Most of the world's cacao grows in countries close to the equator，with over half of it growing in the African nations of Ghana and Ivory Coast.

It's predicted that by 2050, climate change will have accelerated the rate at which temperatures in these countries rise, making it extremely difficult for cacao to grow there.

    The problem doesn't lie in increased heat, however，but in lower humidity (湿度)，as it's believed that rainfall will stay at the same level if the temperature rises.

    “In other words, as higher temperatures squeeze more water out of soil and plants, it's unlikely that rainfall will increase enough to offset the moisture (含水量) loss,” Michon Scott, the essay's author, wrote.

    To help fight this problem, researchers from Berkeley University in the US are working on changing the DNA of cacao plants to allow them to survive in dryer conditions by using gene editing technology, according to US News.

    In the meantime, US company Mars, one of the world's biggest manufacturers of chocolate products, announced in January that it would spend $1 billion to help reduce the effects of climate change.

    “This is a world issue, and it requires everyone to work together,” Mars spokesperson Barry Parkin told Business Insider.

    The message here is that if we all do our part, we may be able to prevent some of the worst impacts of climate change. Or if we're unlucky, chocolate will become a thing of the past.

    Researchers have been investigating for years the ways in which screens affect the quality of a person's reading. The magazine Scientific American reported that at least 100 studies have been published on the issue since the 1980s.

    Virginia Clinton carried out a research examination. She is a professor of Education, Health and Behavior at the University of North Dakota. She found what she called a "small but significant" difference in reading text from screen versus paper.

    Clinton looked at 33 past studies that examined paper versus screen reading. All of the studies were done between 2008 and 2018. The studies collectively had 2,799 study subjects, including both children and adults. Clinton's examination found that reading from paper generally led to better understanding and improved a person's performance on tests connected to the reading material. And, she found no major differences in reading speed between the two.

    Clinton and other researchers have found screen readers often believe they understand a text better than they really do. And, they are more likely than paper readers to overestimate how well they would do on a test of the materials they have read.

    Yet, this overestimated sense of understanding is especially common among screen readers. Clinton said, "There are many possible reasons for such findings. Overconfidence of reen readers, for example, could be the result of a distracted, less focused mind. Readers' preferences are also important. Research shows the majority of people of all ages prefer reading from paper. If you are enjoying the reading process, you're going to be more involved. You're going to be paying better attention. Preferences are a key issue here."

    Several studies have found that people often think of paper materials as something more important and serious. "If you are reading from paper, your mind thinks this is something important. I need to pay attention to it," Clinton said.