If you can find a tree which has been cut down，you will see many rings，or circles，on the base of the trunk.By learning to read these rings，you can find out about the tree's life.

    The number of rings tells you how old the tree is.Each year，new wood is formed on the outside of the tree.This new wood is light in color when the tree is growing in spring and summer，and dark in winter when the tree is not growing much.So，if you count the rings of dark­or­light colored wood，you can often find out how old the tree is.

    You can also tell which years have been good years and which years have been bad years.When the light­colored rings are very wide，it means that the tree has been growing quickly that year.If the rings are narrow，it has been growing slowly.If the rings on a tree trunk were greatly magnified，you would be able to see why the rings are light­colored when the tree is growing quickly and dark­colored when the tree is growing slowly.The tree trunk is made up of microscopic tubes，like some pipes，carrying water from the soil，through the trunk，and up to the leaves.They are wide and thin­walled when the tree is growing quickly and they are carrying a lot of water.They are narrow and stuck together when the tree is not growing so quickly.

    When a tree is old，the tubes in the centre of the tree don't carry water.The walls of the tubes have become thick with materials which have stuck along them over the years，forming a kind of wood called“heartwood”．This kind of wood is darker in color than the young，growing wood on the outside of the tree.

    You don't very often see whole tree trunks which have been cut across.But once you learn to read a cross section of the wood，you can see much more in wood which has been used to make boxes，houses and other things.

    In most wood，instead of seeing the trunk cut across，you are seeing it cut along its length.Because you don't see the whole tree，you can't tell how old it is.

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                                                                       Balloon Volleyball

    It's a rainy, dark day and there's nothing to do. You don't feel like sitting quietly but you are not allowed to make a lot of noise. What can you do for fun? Try balloon volleyball.

    Items needed for this game: a balloon (or two, in case the first one bursts), some ropes, two chairs, at least two people and a room.

    Set up the room. If you're in the living room, or a family room, be sure to move all the furniture out of the way. Get two chairs and set them in the middle, outer edges(边缘)of the room. They should be at the same place where you put a volleyball net. Turn them so that the seat is facing the wall, not the “playing” space. Tie the rope onto the top of the chair, and run the rest of the rope to the other chair. Now tie it on this chair at the same place as the first chair. You can decide the “out-of-bounds”(出界) lines, if you want to have them, but they really are not necessary in this game.

    Blow up the balloon. Choose sides. You will play this game on your knees (at least until they start hurting and you want to stand). Each side must get the balloon over the rope in three hits. If it does not get over, the other side gets the balloon and a point. This game becomes more difficult because you must play without talking.

    You can also add other rules to make it more difficult; for example, you can only use your left hand or only your right hand to hit the balloon.

    Continue playing until one side gets 10 points. You can make your game longer or shorter by changing the number of points it takes to win.

    This is a fun way to get your energy out, have fun, and not make too much noise on a rainy, stay-in-the-house day.

    There are a growing number of pet owners who feed their pets on raw foods, which means "uncooked" meat and bones. William Burk, a pet food specialist from the Food and Drug Administration(FDA), believes that feeding raw meat to pets is against its goal of protecting the public from health dangers, and that raw meat and bones do not have all the required nutrition that a pet needs every day.

    Recognizing how popular these foods are, the FDA has provided guidelines for producers of pet foods which contain uncooked meat for dogs, cats and other pets. The guidelines give rules to protect pet owners and pets from dangers about food safety and lack of nutrition.

    Pet owners who feed raw meat and bones to their pets should deal with these products very carefully to protect themselves against possible dangers, says Burk. Just as when you are preparing foods for human beings, use hot water and soap to wash your hands, containers, and surfaces that come into contact with the food. Don't put your hands near your mouth until you have washed them, and don't allow your pet to touch your face right after it has eaten raw meat.

    "If pet owners choose to feed bones to their pets, they should watch their pets carefully when they are eating bones," Burk says, "If a pet eats a big piece of bone that won't pass through its digestive system(消化系统), it is likely to kill the pet."

    This year's flu season is pretty scary. To try to minimize the effects, public officials are still urging anyone who hasn't yet gotten their flu shot to get one as soon as possible. However, even if every single person got a shot in the arm, the vaccine(疫苗)—with its excellent 36 percent effectiveness—would not prevent everyone from getting infected with the annoying virus. Knowledge is power, so here's what goes on in your body when you come down with the flu.

    The influenza virus primarily attacks your nose, throat, and the tubes that lead to your lungs. But the flu is so much more than that. Your muscles ache, your head hurts, and your appetite goes down, among other things. To our surprise, almost all of these symptoms have less to do with the virus itself than with your immune(免疫的)response to them. Unfortunately, the very defense you have in place to get rid of the flu is the reason you feel so painful when you recover.

    The virus usually enters through your mouth, typically by way of your hands But it takes a few days for symptoms to set in. While this process might cause some harm to your nose and throat, it's nothing major, and nothing like the symptoms that typically accompany a bad or even mild case of the flu.

    The real fun starts when your immune system begins to fight. Your immune system comes in two parts: the innate system and the adaptive. The innate immune system is essentially an all-purpose tool. As soon as your body senses the presence of any injury or invader (入侵者), the innate immune system launches into action by producing tiny proteins called cytokines and chemokines. The cytokines reproduce almost immediately and start to attack the virus. This increase in immune cells creates an serious inflammation(炎症) throughout the body. But the worst is still to come. Meanwhile, the chemokines work with the adaptive immune system to help create T cells. These cells are a special type of white blood cell that works in a much more specific way: They find the influenza virus, identify what's special about it, and create something unique on their surface that finds and destroys similar invaders.

    Learning Chinese could be one of the most important decisions you ever make. Chinese is becoming the language to learn in the 21^st century. With the world's largest population and a rapidly growing middle class, China stands to become the engine of the world's economy in the coming years. This will make learning Chinese very important for people in many industries, or for those of us who wish to visit China or learn from its culture and history.

    There is an ongoing effort to modernize the writing system and standardize the language. An increasing number of people learning Chinese are learning the Mandarin, so unless you absolutely need to learn another dialect (such as Cantonese), be sure you are studying Mandarin.

For native English speakers Chinese is one of the most difficult and most different languages to learn. The vocabulary is wholly unfamiliar and unlike anything we know. In addition, in the Chinese tone system, words are spoken in rising or falling tones, which help to distinguish between them. Furthermore, there is the Chinese writing system— a collection of thousands of individual ideograms (表意文字), or symbols, which represent a word or an idea. These ideograms have no phonetic value—that is to say, we can't tell how the word is pronounced by how it is written. There is a method to present written Chinese in a phonetic script called pinyin. If you are learning Chinese, you'll be working with this pinyin system, but the beauty of the traditional writing system shouldn't be passed up. All these factors make learning Chinese difficult for us. Yet, for a determined learner, there's always a way to overcome it.

    Some of the best research on daily experience is rooted in rates of positive and negative interactions, which has proved that being blindly positive or negative can cause others to be frustrated or annoyed or to simply tune out.

    Over the last two decades, scientists have made remarkable predictions simply by watching people interact with one another and then scoring the conversations based on the rate of positive and negative interactions. Researchers have used the findings to predict everything from the likelihood that a couple will divorce to the chances of a work team with high customer satisfaction and productivity levels.

More recent research helps explain why these brief exchanges matter so much. When you experience negative emotions as a result of criticism or rejection, for example, your body produces higher levels of the stress hormone, which shuts down much of your thinking and activates(激活) conflict and defense mechanisms(机制). You assume that situations are worse than they actually are.

    When you experience a positive interaction, it activates a very different response. Positive exchanges increase your body's production of oxytocin, a feel-good that increases your ability to communicate with, cooperate with and trust others. But the effects of a positive occurrence are less dramatic and lasting than they are for a negative one.

    We need at least three to five positive interactions to outweigh every one negative exchange. Bad moments simply outweigh good ones. Whether you're having a conversation, keep this simple short cut in mind: At least 80 percent of your conversations should be focused on what's going right.

    Workplaces, for example, often see this. During performance reviews, managers routinely spend 80 percent of their time on weaknesses and "areas for improvement". They spend roughly 20 percent of the time on strengths and positive aspects. Any time you have discussions with a person or group, spend the vast majority of the time talking about what is working, and use the remaining time to address weaknesses.