A black hole is created when a large star burns out. Like our sun, stars are unbelievably hot furnaces(熔炉) that burn their own matter as fuel. When most of the fuel is used up, the star begins to die.

    The death of a star is not a quiet event. First there is a huge explosion. As its outer layer is blasted off into space, the dying star shines as brightly as a billion suns.

    After the explosion, gravity pulls in what's left of the star. As the outside of the star sinks toward the center, the star gets smaller and smaller. The material the star is made of becomes tightly packed together. A star is so solid that a teaspoon of matter from it weighs billions of pounds.

    The more the star shrinks(收缩), the stronger the gravity inside it becomes. Soon the star is very tiny, and the gravity pulling it in is unbelievably strong. In fact, the gravity is so strong that it even pulls light into the star! Since all the light is pulled in, none can go out. The star becomes black when there is no light. Then a black hole is born!

    That's what we know about black holes. What we don't know is this: What happens inside a black hole after the star has been squeezed into a tiny ball? Does it keep getting smaller and smaller forever? Such a possibility is hard to imagine.

    But if the black hole doesn't keep shrinking, what happens to it? Some scientists think black holes are like doorways to another world. They say that as the star disappears from our universe, it goes into another universe. In other words a black hole in our universe could turn into a "white hole" in a different universe. As the black hole swallows(吞噬) light, the white hole shines brightly--somewhere else. But where? A different place, perhaps, or a different time--many years in the past or future.

    Could you travel through a black hole? Right now, no. Nothing we know of could go into a black hole without being crushed(挤压). So far the time being, black hole must remain a mystery.

Black holes are a mystery--but that hasn't stopped scientists from dreaming about them. One scientist suggested that in the future we might make use of the power of black holes. They would supply all of Earth's energy needs, with plenty to spare. Another scientist wondered if a black hole could some day be used to swallow earthly waste--a sort of huge waste disposal(处理) in the sky!

    When it comes to medical care, many patients and doctors believe “more is better.” But what they do not realize is that overtreatment—too many scans, too many blood tests, too many procedures—may bring harm. Sometimes a test leads you down a path to more and more testing, some of which may be attacking, or to treatment for things that should be left out.

    Terrence Power, for example, complained that after his wife learned she had Wegener's disease, an uncommon disorder of the immune system(免疫系统), they found it difficult to refuse testing recommended by her doctor. The doctor insisted on office visits every three weeks, even when she was feeling well. He frequently ordered blood tests and X-rays, and repeatedly referred her to experts for even minor complaints. Even when tests came back negative, more were ordered, and she was hospitalized as prevention when she developed a cold. She had as many as 25 doctor visits during one six-month period. The couple was spending about $30,000 a year for her care.

    After several years of physical suffering and near financial ruin from the medical costs, the couple began questioning the treatment after discussing with other patients in online support groups. “It's a really hard thing to determine when doctors have crossed the line,” Mr. Power said. “You think she's getting the best care in the world, but after a while you start to wonder: What is the purpose?” Mr. Power then spoke with his own primary care doctor, who advised him to find a new expert to oversee Mrs. Power's care. Under the new doctor's care, the regular testing stopped and Mrs. Power's condition was stable. Now she sees the doctor only four or five times a year.

    Having good etiquette(礼节，礼仪) at the workplace is very important to be a favorite in an office. However, many people aren't aware of the workplace etiquette and this creates a very bad impression in the office. So it's important to know some workplace etiquette tips.

    Among all the workplace etiquette guidelines, the most important is to be punctual(准时的) to your office. Though going late due to an emergency is okay, habitual late comers are never appreciated in any organization. By arriving at your office on time, you show that you're aware of your responsibilities and have respect for the organization. In case you feel that you would be late, call the concerned authority and report the matter to him or her.

    Also, a proper knowledge of the workplace email etiquette is a must. In the official emails, you need to mention the subject concisely (简洁地), while at the same time include all the important details which are to be shared. You should use good and grammatically correct language while writing emails.

    A knowledge of telephone etiquette in the workplace is very important as well. While talking on the telephone, be polite and listen to what they're saying carefully. Only then should you say what you feel. Speak in a voice which would be heard clearly at the other end.

    The workplace guidelines are important even while you're dining or celebrating with your co-workers. If you get a call in between, receive it after you're permitted by the others by saying "excuse me". Don't talk loudly while eating. Greet people well and try to make them feel comfortable, while being in your company.

    These guidelines will help you become the best employee of a company. All the best!

    From American Express, wedding guests will, on average, spend $673 on each wedding they attend this year. It includes airfare （$225）, hotel （$170）, dining out （$116）and dressing up （$95）and the gift. If you have weddings to attend this year, here are some tips for you to avoid breaking the bank.

    ⒈Book flights in advance

    The moment you decide to attend a wedding is the time to check flight prices at the best time. Plane fares are higher in the summer, especially in July and August. Booking in advance will save you money, as will watch for sales on lower﹣cost carriers like JetBlue and Frontier. You can check Google Flights for a calendar of prices showing the cheapest days to fly from apps like Hopper to get real﹣time alerts when a fare is at its lowest price point.

    ⒉Don't blow your budget on the gift

    If you've got the money, an expensive gift is lovely. But there's no need to take out loans to prove your love for the happy couple. Skip an expensive necklace by giving （an appropriate amount of） cash instead. To save on the gift, consider making one： A photo album or scrapbook of memories with the bride and groom shows how much you care. You could also share the gift with other guest(s) or even make gifts with DIY ideas by yourself to save money.

    ⒊Use old dresses and suits

    You don't always have to be on a new dress for a wedding. While men have the option of repeating their suits, women are more likely to spend money on new clothes for the special occasion. But before you take out your wallet, consider reinventing something already in your closet. Belts, colorful scarves, shoes can bring life to any outfit.

    Life is difficult.

    What do you think about life? Maybe most people say that life is difficult. But life is no longer difficult once we truly understand and accept it. Most people do not fully see this truth. Instead, they complain about their problems and difficulties as if life should be easy. It seems to them that their difficulties represent a special kind of suffering especially forced upon (强加于) them or their families, their class, or even their nation.

    What makes life difficult is that the process of facing and solving problems is a painful one. Problems, depending on their nature, cause us sadness or loneliness or regret or anger or fear. These are uncomfortable feelings, often as painful as any kind of physical pain. And since life causes an endless series of problems, life is always difficult and is full of pain as well as joy.

    Yet, it is in this whole process of solving problems that life has its meaning.

    Problems are the serious test that tells success from failure. When we desire to encourage the growth of the human spirit, we encourage the human ability to solve problems, just as in school we set problems for our children to solve. It is through the pain of meeting and working out problems that we learn. As Benjamin Franklin said, "Those things that hurt instruct." It is for this reason that wise people learn not to fear but to welcome the pain of problems.