It is bad to have food stuck between your teeth for long periods of time. This is because food attracts germs; germs produce acid, and acid hurts your teeth and gums. Flossing (使用牙线) helps to remove the food that gets stuck between your teeth. This explains why flossing helps to keep your mouth healthy, but some doctors say that flossing can also be good for your heart.

    It may seem strange that something you do for your teeth can have any effect on your heart. Doctors have come up with a few ideas about how flossing works to keep your heart healthy. One idea is that the germs that hurt your teeth can leave the mouth and travel into your blood.Germs that get into the blood can then attack your heart. Another idea is based on the fact that when there are too many germs in your mouth, the body tries to fight against there germs. For some reason, the way the body fights these mouth germs may end up weakening the heart overtime.

    Not every doctor agrees about these ideas. Some doctors think that the link between good flossing habits and good heart health is only a coincidence. The incidence (发生率) of two or more events is completely random, as they do not admit of any reliable cause and effect relationship between them. For example, every time I wash my car, it rains. This does not mean that when I wash my car, I somehow change the weather. This is only a coincidence. Similarly, some doctors think that people who have bad flossing habits just happen to also have heart problems, and people who have good flossing habits just happen to have healthy hearts.

    The theory that flossing your teeth helps to keep your heart healthy might not be true. But every doctor agrees that flossing is a great way to keep your teeth healthy. So even if flossing does not help your heart, it is true to help your teeth. This is enough of a reason for everyone to floss their teeth every day.

    You might think that “global warming” means nothing more than a rise in the world's temperature. But rising sea levels caused by it have resulted in the first evacuation (撤离) of an island nation, the citizens of Tuvalu will have to leave their homeland.

    During the 20th century, sea level rose 8~12 inches. As a result, Tuvalu has experienced lowland flooding of salt water that has polluted the country's drinking water.

    Paani Laupepa, a Tuvaluan government official, reported to the Earth Policy Institute that the nation suffered an unusually high number of fierce storms in the past ten years. Many scientists connect higher surface water temperatures resulting from global warming to greater and more damaging storms.

    Laupepa expressed dissatisfaction with the United States for refusing to sign the Kyoto Protocol, an international agreement calling for industrialized nations to reduce their greenhouse gas emissions (排放), which are a main cause of global warming. “By refusing to sign the agreement, the US has effectively taken away the freedom of future generations of Tuvaluans to live where their forefathers have lived for thousands of years.” Laupepa told the BBC.

    Tuvalu has asked Australia and New Zealand to allow the gradual move of its people to both countries.

    Tuvalu is not the only country that is vulnerable (易受影响的) to rising sea levels. Maumoon Gayoon, president of the Maldives, told the United Nations that global warming has made his country of 311,000 an “endangered nation”.

    It is important to know another language and how to communicate without words when you are in another country. Before saying anything, people communicate with each other by using gestures(手势). However, many gestures have different meanings, or no meaning at all, in different parts of the world.

    In the United States, nodding your head up and down means "yes", while in some parts of Greece and Turkey, it means "no". In the southeast of Asia, it is a polite way of saying "I heard you".

    Today in the USA, when someone puts his thumb up, it means "Everything is all right." However, in Greece it is bad. Also putting your clasped(紧握的)hands up above your head means "I am the winner." It is the sign which players often make. In Russia it is the sign of friendship.

    In the USA, holding your hand up with the thumb and index finger(食指), and the other three straight means "Everything is OK." In France, it means "You are worth nothing."

    It is also important to make eye communication. If you look down when talking to an American, he or she may feel that you are shy, or you are trying to hide something.

Besides these, you should also know there are some topics that cannot be talked about, such as age, weight and marriage. You can talk about the weather, work, sports, food, where one lives and news of the day.

    Some spiders hunt on the ground, others build webs to trap their food, but the grass water spider catches its prey by running along the surface of the water.

    This special water spider lives on the grassy banks of streams where mosquitoes, damsel flies and other insects come to feed and breed.

    Although it is one of the largest spiders in New Zealand, it has an unusual ability. It doesn't disturb the water as it waits for its meal, and there is barely a ripple(波纹) when it skims(掠过) across the surface at lightning speed to catch its prey.

    Grass water spiders deal swiftly with larger insects like damsel flies by pulling their heads under the water and holding them there until they drown.

    After a meal, the grass water spider spends up to half an hour grooming(修饰) itself. It wipes its eight eyes, brushes its antennae(触角), and takes special care to clean the hairs on its body.

    It is the hairs that trap tiny bubbles(泡沫) of air so that the spider can run down a blade(叶片) of grass and stay underwater for up to an hour when it is frightened. The hairs also keep the spider dry, even underwater.

    It is only when the female spider is caring for the young that she does not hunt on the water. After mating, she produces a large egg sac(囊), which she carries around for five weeks. Once the eggs start to hatch, she attaches the sac to some blades of grass or a thistle. She then tears the sac open and releases the tiny spiders into the nursery web.

    The UK has a well­respected higher education system and some of the top universities and research instructions in the world. But to those who are new to it all, sometimes it can be confusing.

    October is usually the busiest month in the college calendar. Universities have something called Freshers' Week for their newcomers. It's a great opportunity to make new friends, join lots of clubs and settle into university life.

    However, having just left the comfort of home and all your friends behind，the prospect(前景) of meeting lots of strangers in big halls can be nerve­wracking (令人焦虑不安的). Where do you start? Who should you make friends with? Which clubs should you join?

    Luckily, there will be thousands of others in the same boat as you worrying about starting their university social life on the right foot. So just take it all in slowly. Don't rush into anything that you'll regret for the next three years.

    Here is some top advice from past students on how to survive Freshers' Week:

    Learn rules. Make sure you know British social etiquette(礼节). Have a few wine glasses and snacks handy for your housemates and friends.

    Be kind. Sometimes cups of tea or even slices of toast can give you a head start in making friends.

    Be sociable. The more active you are，the more likely you'll be to meet new people than if you're someone who never leaves his room.

    Bring a doorstop. Keep your door open when you're in and that sends positive messages to your neighbors that you're friendly.

    So with a bit of clever planning and effort, Freshers' Week can give you a great start to your university life and soon you'll be passing on your experience to next year's new recruits.

    You don't need to get in a time-traveling machine to see how technology will reshape our lives, such as the way we shop. Several new technologies that are to change your buying habits already exist. Let's see what's waiting for your future shopping.

    Try it on, virtually(虚拟的). Want to shop online for a new pair of eyeglasses? You don't need to guess which pair looks best on you. Go and see the eBay Fashion iPhone app to try a pair of eyewear you're checking out on a picture of your face. But what if you want to buy something bigger? Thanks to Microsoft Kinect's motion tracking camera, you can cover clothes on your screen body. You can even choose the background of your virtual fitting room to enrich your shopping experience.

    Get a perfect, custom fit. Everyone's body is shaped differently. To get a perfect fit, you sometimes have to get your clothes changed. But by using 3D scanning(扫描) technology, all the clothes you buy will fit your body perfectly. Some companies scan your body using High-tech to get the most exact sizes, so they can make special clothes just for you.

    Experience high-tech shopping carts and checkout counters. High-tech shopping carts could, in time, be a common sight in malls and supermarkets. Microsoft Kinect-enabled carts are under test at present. The cart can follow you along the aisles (通道), controlled only by your movement and your voice. In China, a supermarket chain(连锁超市) introduced tablet-equipped carts that guide shoppers around the stores' aisles.

    In the United States, several supermarkets use a device(装置) called Scan It that gives buyers the freedom to scan goods on their own while they shop. While it's great not having to line up at a checkout counter, we wouldn't mind it if the store used Toshiba's new Object Recognition Scanner. The machine identifies(辨认) a product as soon as it's placed in front of a camera just by its shape and color, even if it has no bar code(条形码).